A selective etching solution for silicon nitride and tungsten

Abstract

The application provides a selective etching solution of silicon nitride and tungsten, which comprises 72-85% of electronic-grade phosphoric acid, 1.25-1.75% of a silicon-containing compound, 0.0263-0.0369% of hydrofluoric acid, 0.02-0.07% of a sulfonic acid substance, 0.1-1.0% of a tungsten etching inhibitor, and the rest is deionized water in percentage by mass. The etching solution can etch silicon nitride faster under the premise that the etching rate (ER) of silicon oxide is less than or equal to 0.96 nm / 30 min, maximally inhibit the etching of metallic tungsten, and ensure that the silicon nitride and the metallic tungsten have a high selectivity ratio.

Description

Technical Field

[0001] This invention belongs to the field of electronic chemicals and relates to an etching solution, particularly a selective etching solution for silicon nitride and tungsten. Technical Background

[0002] 3D NAND technology, as a relatively new flash memory technology, achieves greater storage capacity and better performance in a smaller storage space through the vertical stacking of storage cells. In its structure, there is a stacking of oxide and metal layers between the vertically oriented storage cells.

[0003] Hot phosphoric acid is often used as an etchant to remove silicon nitride in wet etching. However, hot phosphoric acid alone has problems such as low etching rate, low selectivity of tungsten, and etching effect on silicon oxide barrier layers.

[0004] To address the aforementioned problems, we attempted to add additives and metal etching inhibitors to the phosphoric acid solution. This aimed to ensure a lower silicon oxide etching rate and faster silicon nitride etching, while simultaneously satisfying the silicon nitride to tungsten selectivity ratio and slowing down the etching of the tungsten layer. Summary of the Invention

[0005] The technical solution of the present invention is a selective etching solution for silicon nitride and tungsten, which ensures that the ER of silicon nitride is ≥5.72nm / min, the ER of silicon oxide is ≤0.96nm / 30min, and the selectivity ratio of silicon nitride to tungsten is maintained, while slowing down the etching of the tungsten metal layer.

[0006] The technical solution of this invention comprises, by mass percentage, 72%-85% electronic-grade phosphoric acid, 1.25%-1.75% silicon-containing compounds, 0.0263%-0.0369% hydrofluoric acid, 0.02%-0.07% sulfonic acid substances, 0.1%-1.0% tungsten etching inhibitor, with the remainder being deionized water.

[0007] Furthermore, the phosphoric acid is electronic grade, with a raw material concentration of ≥85% and a metal ion content of ≤0.02ppm.

[0008] Furthermore, inorganic silica and fluoride ions combine in solution to form fluorosilicic acid, which easily decomposes at high temperatures to generate silicon tetrafluoride gas, resulting in a decrease in fluoride ion content and a poorer etching life.

[0009] Organosilanes can combine with fluoride ions in solution without forming silicon tetrafluoride. However, silanes with poor water solubility are easily precipitated from solution after combining with fluoride ions. Therefore, it is necessary to select silanes with hydrophilic end groups.

[0010] Furthermore, the silicon-containing compound is one or a combination of several silane coupling agents such as mercaptopropyltriethoxysilane, 3-[bis(2-hydroxyethyl)amino]propane-triethoxysilane, and diethylphosphorylethyltriethoxysilane.

[0011] Furthermore, the tungsten etching inhibitor is one or more of N-octylpyrrolidone, L-lysine, biotinylate-4-aminobutyric acid, dimethyloldihydroxyvinylurea, and N,N'-carbonyldiimidazole. These tungsten etching inhibitors possess unshared free electrons, which can bind to the empty orbitals of metallic tungsten through coordination bonds, thereby forming a protective layer on the surface of the metallic tungsten.

[0012] Furthermore, the fluorine content in the solution ranges from 250 ppm to 350 ppm. A low fluorine content results in an excessively low silicon nitride etching rate, thus reducing the selectivity ratio between silicon nitride and tungsten. A high fluorine content results in an excessively high silicon oxide etching rate.

[0013] Furthermore, the molar ratio of silicon to fluorine is in the range of 3.2-4.8. A too-low fluorine-silicon ratio will decrease the etching rate of silicon nitride and increase the thickness of silicon oxide. A too-high fluorine-silicon ratio will increase the etching rate of silicon nitride while significantly increasing the etching rate of silicon oxide.

[0014] Furthermore, sulfonic acid substances can synergistically work with hydrofluoric acid to promote the etching of silicon nitride.

[0015] Furthermore, the etching solution has an ER of ≥5.72nm / min for silicon nitride and an ER of ≤0.96nm / 30min for silicon oxide.

[0016] Furthermore, the etching rate ratio of silicon nitride to tungsten in the etching solution is greater than 400, and the ER of tungsten is ≤0.476nm / min.

[0017] Furthermore, the preferred operating temperature range for the etching solution is 110°C-140°C, more preferably 120°C-130°C, and most preferably 125°C.

[0018] The present invention has the following beneficial effects:

[0019] The main acidic substance phosphoric acid used in the etching solution of this invention has a good selective etching effect on silicon nitride.

[0020] The addition of fluorine in this invention improves the etching rate of silicon nitride, thereby increasing the selectivity ratio of silicon nitride to tungsten.

[0021] The addition of silicon in this invention allows the silica formed after etching to re-adhere to the silicon oxide surface, thus slowing down the etching rate of silicon oxide and resulting in an ER of silicon oxide ≤ 0.96 nm / 30 min.

[0022] In this invention, the addition of sulfonic acid substances can synergistically promote the etching of silicon nitride with hydrofluoric acid.

[0023] The free electrons of the tungsten etching inhibitor introduced in this invention can form a protective layer on the surface of tungsten metal through coordination with the empty orbitals of tungsten metal, thereby reducing the etching rate of tungsten and playing a protective role. Specific implementation methods

[0024] The following will describe in detail the implementation process of this invention. The implementation process is only used to deepen the understanding of the invention and does not limit the scope of the invention.

[0025] Example 1

[0026] A selective etching solution for silicon nitride and tungsten, wherein electronic-grade phosphoric acid contains 72% by mass, KH-580 contains 1.5% by mass, hydrofluoric acid contains 0.0316% by mass, biotin 3-sulfonic acid-N-hydroxysuccinate contains 0.05% by mass, N-octylpyrrolidone contains 0.5% by mass, and the remainder is deionized water.

[0027] Prepare 100g of etching solution according to the above formula, and place it in a 100ml round-bottom three-hole flask. Add a stir bar to the flask, set the electric heating pot temperature to 125℃, and the stirring rate to 450r / min. When the solution temperature reaches and stabilizes at 125±0.5℃, etch the silicon nitride wafer (the silicon nitride wafer is a silicon substrate with a thickness of approximately 110nm). Before etching, cut the silicon nitride wafer into 2*1cm pieces. To avoid the influence of the oxide layer on the surface of the sample on the experimental results, soak the sample in a 200:1 HF solution for 40s, then rinse with water for 10s, and dry with nitrogen. Measure the initial thickness of the sample using an ellipsometry, taking two measurements and using the arithmetic mean. Immerse the sample in the etching solution for 5min, rinse with water, and dry with nitrogen. Measure the thickness of the sample after etching using an ellipsometry, taking two measurements and using the arithmetic mean. The calculated etching rate of silicon nitride is 6.93nm / min.

[0028] Prepare 100g of etching solution according to the above formula, and place it in a 100ml round-bottom three-hole flask. Add a stir bar to the flask, set the electric heating pot temperature to 125℃, and the stirring rate to 450r / min. When the solution temperature reaches and stabilizes at 125±0.5℃, etch the silicon oxide wafer (the silicon oxide wafer is a silicon substrate with a thickness of approximately 30nm). Before etching, cut the silicon oxide wafer into 2*1cm pieces. To avoid the influence of the oxide layer on the surface of the sample on the experimental results, soak the sample in the etching solution for 10min beforehand, rinse it with clean water, and dry it with nitrogen. Measure the initial thickness of the sample using an ellipsometry, taking two measurements and using the arithmetic mean. Immerse the sample in the etching solution for 30min, rinse it with clean water, and dry it with nitrogen. Measure the thickness of the sample after etching using an ellipsometry, taking two measurements and using the arithmetic mean. Calculations show that the silicon oxide thickening can be achieved at an etching rate of -0.096nm / 30min.

[0029] Prepare 100g of etching solution according to the above formula, and place it in a 100ml round-bottom three-hole flask. Add a stir bar to the flask, set the electric heating pot temperature to 125℃, and the stirring rate to 450r / min. When the solution temperature reaches and stabilizes at 125±0.5℃, etch the tungsten sheet (its thickness is approximately 88nm). Before etching, cut the tungsten sheet into regular 2*2cm square pieces. To avoid the influence of the oxide layer on the surface of the sample on the experimental results, rinse the sample with clean water beforehand and then dry it with nitrogen. Use a four-probe to measure the initial thickness of the sample, measure four times, and take the arithmetic mean. Immerse the sample in the etching solution for 30min, rinse it with clean water, and dry it with nitrogen. Use a four-probe to measure the thickness of the sample after etching, measure four times, and take the arithmetic mean. The calculated etching rate of the metal is 0.075nm / 30min.

[0030] The above experimental results show that the etching solution formulation has an ER ≥ 5.72 nm / min for silicon nitride and an ER ≤ 1 nm / 30 min for silicon oxide. Furthermore, the etching rate ratio of silicon nitride to tungsten in this etching solution is greater than 400, and the ER of tungsten is ≤ 0.5 nm / 30 min.

[0031] Subsequent experiments were conducted by varying the contents of phosphoric acid, fluorine, biotin 3-sulfonic acid-N-hydroxysuccinate, the molar ratio of silicon to fluorine, the type and content of silane coupling agents, and the type and content of tungsten etching inhibitors. Table 1 shows the relevant formulations for Examples 1-17 and Comparative Examples 1-6.

[0032] Table 1 Experimental formulation

[0033]

[0034]

[0035]

[0036] Table 2 shows the experimental results and selection ratios of Examples 1-17 and Comparative Examples 1-6.

[0037]

[0038]

[0039] Note: Negative numbers in the table indicate the rate of silicon dioxide thickening.

[0040] From the experimental data and selectivity ratios in Table 2, it can be seen that, compared with Example 1, Comparative Example 1, using only 72% electronic-grade phosphoric acid and 1.5% KH-580 as the etching solution, showed a lower etching rate for silicon nitride and a higher etching rate for tungsten, resulting in a very low selectivity ratio between silicon nitride and tungsten. Comparative Example 2, compared with Example 1, did not add silicon, resulting in an increased etching rate for silicon nitride and a significantly increased etching rate for silicon oxide, with little effect on the etching of tungsten. Comparative Example 3, compared with Example 1, reduced the fluorine content in the etching solution, resulting in a lower etching rate for silicon nitride and a more significant increase in silicon oxide thickness, indicating that within a certain range, fluorine can increase the etching rates of both silicon nitride and silicon oxide. Comparative Example 4, compared with Example 1, did not add a metal etching inhibitor, resulting in a significantly faster etching rate for tungsten, with little effect on the etching rates of both silicon nitride and silicon oxide. In Comparative Example 5, 3-thiocyanopropyltriethoxysilane itself has poor water solubility. After reacting with hydrofluoric acid, it forms a fluorosilicon compound with even poorer water solubility, which precipitates out of the etching solution. This leads to a decrease in the silicon and fluorine content of the etching solution, resulting in an increased silicon oxide etching rate and a decreased silicon nitride etching rate. In Comparative Example 6, compared to Example 1, biotin-3-sulfonic acid-N-hydroxysuccinate was not added to the etching solution. The silicon nitride etching rate decreased, the etching rate difference between silicon oxide and tungsten was not significant, and the selectivity ratio of silicon nitride to tungsten decreased.

[0041] The type and content of silane coupling agent were changed. Because of its poor nucleation ability with fluorine, the etching rate of silicon nitride was slower, while the etching rate of silicon oxide was faster, and the inhibitory effect on tungsten metal was not obvious.

[0042] In Example 1, the silicon element in the silane coupling agent inhibits the etching of silicon oxide, slowing down the etching rate within a certain range. The fluorine element in hydrofluoric acid promotes the etching of silicon nitride. Biotin-3-sulfonic acid-N-hydroxysuccinate works synergistically with hydrofluoric acid, and N-octylpyrrolidone acts as a metal etching inhibitor, resulting in an etching rate of 0.075 nm / 30 min for tungsten. The selectivity ratio of silicon nitride to tungsten reaches 2770, indicating a high selectivity. Subsequently, the silicon-to-fluorine ratio, fluorine content, type and content of metal etching inhibitors, and type and content of silane coupling agents were adjusted within a certain range. The experimental results showed that the selectivity ratio of silicon nitride to tungsten was greater than 400, and the ER of tungsten was ≤0.5 nm / 30 min. The results indicate that when the silicon-to-fluorine ratio exceeds a certain value or / and the fluorine content is excessive, silicon oxide etching becomes too rapid.

[0043] Naturally, the embodiments described above are for illustrative purposes only and not as limitations on the implementation. Different combinations of the features described above are permissible. The technical embodiments described in the claims are within the scope of protection. Furthermore, variations in proportions and equivalent substitutions or recombinations of raw materials are also within the scope of protection of this invention.

Claims

1. A selective etching liquid for silicon nitride and tungsten, characterized by: By mass percentage, it includes 72%-85% electronic-grade phosphoric acid, 1.25%-1.75% silicon-containing compounds, 0.0263%-0.0369% hydrofluoric acid, 0.02%-0.07% sulfonic acid substances, 0.1%-1.0% tungsten etching inhibitor, and the remainder is deionized water. The silicon-containing compound is one or a combination of several of γ-mercaptopropyltriethoxysilane (KH-580), 3-[bis(2-hydroxyethyl)amino]propane-triethoxysilane, and diethylphosphorylethyltriethoxysilane; The tungsten etching inhibitor includes one or more of N-octylpyrrolidone, L-lysine, biotinylate-4-aminobutyric acid, dihydroxymethyldihydroxyvinylurea, and N,N'-carbonyldiimidazole. The sulfonic acid substance is biotin-3-sulfonic acid-N-hydroxysuccinate.

2. The selective etching solution for silicon nitride and tungsten according to claim 1, characterized in that, Phosphoric acid is electronic grade, with a raw material concentration of ≥85% and a metal ion content of ≤0.02ppm.

3. The selective etching solution for silicon nitride and tungsten according to claim 1, characterized in that: The fluorine content in the solution ranges from 250 ppm to 350 ppm.

4. The selective etching solution for silicon nitride and tungsten according to claim 1, characterized in that: The molar ratio of silicon to fluorine in the solution ranges from 3.2 to 4.

8.

5. The selective etching solution of silicon nitride and tungsten according to any one of claims 1-4, characterized in that: The etching solution can be used in a temperature range of 110℃-140℃.

6. The selective etching solution for silicon nitride and tungsten according to claim 5, characterized in that: The etching solution can be used in a temperature range of 120℃-130℃.

7. The selective etching solution for silicon nitride and tungsten according to claim 6, characterized in that: The etching solution is designed for use at a temperature of 125°C.

8. The selective etchant for silicon nitride and tungsten according to any one of claims 1-7 is used in etching semiconductor materials containing silicon nitride and tungsten.

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