Selective etching solution for silicon nitride and silicon oxide
By adding components such as silicon oxide inhibitors, silane dispersants, and etching stabilizers to the alkaline etching solution, the problem of insufficient selectivity of silicon nitride and silicon oxide in 3D NAND manufacturing is solved, achieving high selectivity and stable etching effect, suitable for high aspect ratio structures.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-20
- Publication Date
- 2026-04-03
AI Technical Summary
In 3D NAND manufacturing, existing alkaline etching solutions lack selectivity when etching silicon nitride and silicon oxide, leading to silica re-adhesion problems and failing to meet the requirements of high stacking layer counts and small channels.
Adding silicon oxide etching inhibitors, silane dispersants, etching stabilizers, and oxygen sacrificial agents to an alkaline system creates a synergistic etching solution that improves the etching rate of silicon nitride and inhibits the etching of silicon oxide.
It achieves high selectivity etching of silicon nitride and silicon oxide, with stable etching rate, suppresses silicon oxide etching, is suitable for high aspect ratio structures, and has excellent process stability and silicon capacity.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of electronic chemicals, and more specifically to a selective etching solution for silicon nitride and silicon oxide. Background Technology
[0002] The development of 3D NAND technology continues to advance towards higher stacking layers, with the industry having already surpassed 500 layers and moving towards 600 layers and beyond. To achieve this goal, technological evolution exhibits three major trends: first, vertical scaling, achieving denser vertical stacking through breakthroughs in key processes such as multi-layer thin-film deposition and high aspect ratio etching; second, lateral scaling, introducing innovative architectures such as vias to replace trenches, increasing storage density while reducing manufacturing costs; and third, multi-dimensional innovation, including the development towards four-layer / five-layer cells to increase single-chip capacity, and exploring more advanced integration technologies such as three-dimensional stacking. These advancements collectively drive the continuous optimization of storage density, performance, and cost-effectiveness to meet the urgent storage needs of data centers, AI, and other applications.
[0003] In 3D NAND manufacturing, it is often necessary to selectively remove the sacrificial layer, which is composed of alternating stacks of silicon nitride and silicon oxide. During traditional high-temperature phosphoric acid etching of SiN / SiO2 stacked structures, the released silica can adhere back to the SiO2 film surface, causing channel blockage or defects in subsequent processes. Although additives such as silica dispersants can alleviate this phenomenon to some extent, as the number of stacked layers increases and the channels become smaller, the physicochemical properties of the phosphoric acid system gradually limit its ability to meet the requirements.
[0004] In alkaline solutions, silicic acid exists primarily as silicate ions, preventing intermolecular condensation and aggregation, thus overcoming the limitation of silicic acid tackiness. However, both SiN and SiO2 in alkaline etching solutions have certain etching rates, leading to insufficient selectivity. Therefore, constructing a SiN / SiO2 high-selectivity solution is of great urgency.
[0005] To address the above problems, there is an urgent need to develop a novel alkaline selective etching solution to achieve efficient and stable etching of silicon nitride while minimizing the erosion of silicon oxide. Therefore, this invention provides a silicon nitride selective etching solution with a stable etching rate by adding silicon oxide etching inhibitors, silane dispersants, and etching stabilizers to an alkaline system. Summary of the Invention
[0006] The main objective of this invention is to provide a selective etching solution for silicon nitride and silicon oxide, thereby solving the problems mentioned in the background art. The etching solution of this invention maintains a high etching rate for silicon nitride while effectively suppressing the etching of silicon oxide, and also possesses a large silicon capacity.
[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A selective etching solution for silicon nitride and silicon oxide, comprising, by mass fraction, 60-70% tris(2-aminoethyl)amine, 1.0-2.0% silicon oxide etching inhibitor, 4.0-5.0% silane dispersant, 0.2-0.3% etching stabilizer, 0.1-0.2% oxygen sacrificial agent, with the balance being deionized water.
[0008] Preferably, the silicon oxide etching inhibitor is one of propyltrimethoxysilane, isopropyltrimethoxysilane, n-butyltrimethoxysilane, isobutyltrimethoxysilane, and tert-butyltrimethoxysilane. Because longer carbon chains provide greater steric hindrance and stronger hydrophobicity, silane coupling agents with 3-4 carbon atoms in their side chains are selected as silicon oxide etching inhibitors to improve the efficiency of inhibiting silicon oxide etching.
[0009] Preferably, the silane dispersant is one of n-propanol, isopropanol, n-butanol, isobutanol, and tert-butanol. To improve the solubility of the silica inhibitor in water, this invention adds a fatty alcohol with a similar side chain group to the inhibitor based on the principle of "like dissolves like".
[0010] Preferably, the etching stabilizer is one of polyvinyl alcohol (Mw=31000-50000), polyethylene glycol 2000, Triton X-100, and Tween 80. The etching stabilizer is a polymer or copolymer with a large molecular weight. It creates steric hindrance and shielding effects through repeating functional groups and hydrophilic / lipophilic ends, allowing the silanols generated by the hydrolysis of the silane coupling agent to arrange themselves relatively orderly in the etching solution, reducing the probability of collisions and thus improving the thermal stability of the etching solution.
[0011] Preferably, the oxygen sacrificial agent is one of ascorbic acid, methyl ethyl ketone oxime, gallic acid, and tert-butylhydroquinone. The oxygen sacrificial agent prevents the tris(2-aminoethyl)amine from being oxidized and decomposed under heating conditions by consuming oxygen or other oxidizing substances in the system.
[0012] Preferably, the etching temperature of the etching solution is 105-120℃. As the etching temperature increases, the etching rate of silicon nitride and silicon oxide gradually increases, but excessively high temperatures will promote the condensation of silanols and their precipitation, as well as the decomposition and deterioration of organic amines. Therefore, the present invention selects an etching temperature of 105-120℃.
[0013] Preferably, the etching selectivity ratio of the etching solution for silicon nitride and silicon oxide is >600.
[0014] Preferably, the etching solution has an etching rate of >16 Å / min for SiN.
[0015] Preferably, when the etching solution dissolves the water-soluble silica compound to a Si concentration of 4000 ppm, no silica re-adhesion or thickening phenomenon will occur on the silicon oxide film, that is, the SiO etching rate is always greater than 0.2 Å / 30 min.
[0016] The second aspect of the present invention provides a method for preparing the selective etching solution of silicon nitride / silicon oxide, characterized by the following steps: first, preparing a tri(2-aminoethyl)amine solution, then sequentially adding an oxygen sacrificial agent, a silane dispersant, an etching stabilizer and a silicon oxide etching inhibitor to the tri(2-aminoethyl)amine solution, and stirring until the etching solution is colorless and transparent to obtain the etching solution.
[0017] A third aspect of the present invention provides the application of the selective etching solution of the silicon nitride / silicon oxide in etching semiconductor materials containing silicon nitride and silicon oxide.
[0018] The etching solution of this invention utilizes tri(2-aminoethyl)amine, which not only provides the alkaline conditions required for etching silicon nitride but also increases the boiling point of the etching solution and accelerates the etching rate by binding water molecules through hydrogen bonds. The silicon oxide inhibitor adsorbs or forms a protective layer on the silicon oxide surface, preventing the condensation precipitation of silanols after silane hydrolysis and significantly suppressing the etching efficiency of silicon oxide. The silane dispersant improves the solubility of the silicon oxide inhibitor, ensuring uniform inhibition within high aspect ratio structures. The etching stabilizer, through steric hindrance and shielding effects, suppresses side reactions and decomposition of components at high temperatures, improving the thermal stability of the etching solution. The oxygen sacrificial agent preferentially reacts with dissolved oxygen, preventing the tri(2-aminoethyl)amine from being oxidized and decomposed under heating conditions, thus extending the service life of the etching solution. Through the combined action of the above substances, the etching solution of this invention simultaneously inhibits the etching of silicon oxide while etching silicon nitride at high speed, achieving a Si3N4 / SiO2 selectivity ratio greater than 600:1 and possessing extremely high silicon capacity.
[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The etching solution of the present invention achieves efficient etching of silicon nitride (>12 Å / min) and significant inhibition of silicon oxide (<1 Å / 30 min) by synergistic use of tri(2-aminoethyl)amine and silicon oxide inhibitor, with a SiN / SiO etching selectivity ratio >600.
[0020] 2. After the etching solution of the present invention dissolves water-soluble silica compounds to a Si concentration of 4000 ppm, the silicon oxide etching rate is still greater than 0.2 Å / 30 min, indicating that the effect of silica on the silicon oxide etching rate is small in the alkaline system, and it has a significant advantage in etching ultra-high aspect ratio structures.
[0021] 3. The etching solution of the present invention, after being placed continuously at the working temperature for 48 hours, exhibits a silicon oxide etching rate fluctuation of no more than 10%, demonstrating excellent process stability. Detailed Implementation
[0022] 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.
[0023] 1. Selective etching solution for silicon nitride / silicon oxide: The preparation method of the etching solution is as follows: At room temperature, an appropriate amount of tri(2-aminoethyl)amine and water are stirred and mixed evenly. Then, the mixture is heated to 60°C. Oxygen sacrificial agent, silane dispersant, etching stabilizer and silicon oxide etching inhibitor are added to the tri(2-aminoethyl)amine solution in sequence. The mixture is stirred until the etching solution is colorless and transparent, thus obtaining the selective etching solution of silicon nitride / silicon oxide.
[0024] Table 1 shows the components and dosages of Examples 1-15 and Comparative Examples 1-3 of the present invention, with the remainder being deionized water.
[0025] 2. Determination of etching rate and silicon capacity of the etching solutions in the examples and comparative examples: (1) Method for detecting etching rate Etching wafers: Silicon nitride and silicon oxide films are directly deposited on the silicon wafer with thicknesses of 1000 Å and 250 Å, respectively; during testing, they are sliced into strips of 1.5 cm * 3 cm.
[0026] Etching time: 360s for silicon nitride etching, 1800s for silicon oxide etching.
[0027] Etching rate calculation method: The film thickness of silicon nitride and silicon oxide before and after etching is detected using an ellipsometry. The film thickness before and after etching is detected 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).
[0028] (2) Method for detecting silicon capacity in etching solution Different doses of water-soluble silica compounds were dissolved in the etching solution until the Si concentration was 1000ppm, 2000ppm, 3000ppm, and 4000ppm. Then the etching solution was adjusted to the working temperature and the etching rate of silicon oxide was measured.
[0029] (3) Etching solution lifetime testing method Timing was initiated from the moment the etching solution was heated to the operating temperature, and the etching rate of silicon oxide was measured every 12 hours until 48 hours. The results are shown in Table 2-4.
[0030] Table 1
[0031] Note: In each example and Comparative Examples 1-3, the content of tris(2-aminoethyl)amine was 65%; Comparative Example 4 was a phosphoric acid-based highly selective silicon nitride etching solution.
[0032] Table 2 Etching Rate and Selectivity
[0033] Table 3 Silicon Capacity of Etching Solution
[0034] Table 4 Etching Solution Lifespan
[0035] As can be seen from Tables 1-4, the 65% tri(2-aminoethyl)amine aqueous solution in Comparative Example 1 exhibited a relatively fast etching rate of 245.22 Å / 30 min for the silicon oxide film at an operating temperature of 115 °C, with an etching selectivity of only 4.6 for SiN / SiO. Based on this, Examples 1-16 further added silicon oxide inhibitors, silane dispersants, etching stabilizers, and oxygen sacrificial agents, reducing the silicon oxide etching rate to below 0.85 Å / 30 min and increasing the SiN / SiO etching selectivity by more than 680.
[0036] Examples 1-5 investigated the effects of different silicon oxide inhibitors under the same conditions. The results showed that, at the same addition amount, tert-butyltrimethoxysilane in Example 5 had the strongest inhibitory effect on the silicon oxide etching rate. This is because the large steric hindrance and strong hydrophobicity of tert-butyl allow tert-butylsilane to form a relatively dense protective layer on the silicon oxide surface, thus inhibiting the etching of silicon oxide.
[0037] Examples 4 and 9-11 investigated the effects of different etching stabilizers under the same conditions. The results showed that as the heating time increased, Comparative Example 3, without the addition of an etching stabilizer, caused the silicon oxide inhibitor to continuously dehydrate, condense, and even precipitate, resulting in a weakened protective effect on silicon oxide and thus a gradual increase in the silicon oxide etching rate; while the formulation with the added etching stabilizer maintained a stable etching rate during the 48-hour heating time.
[0038] Examples 4 and 12-14 investigated the effects of different oxygen sacrificial agents under the same conditions. The results showed that the formulation without an oxygen sacrificial agent was the best. With increasing heating time, in Comparative Example 2, due to the absence of an oxygen sacrificial agent, tris(2-aminoethyl)amine was gradually oxidized and decomposed, the alkalinity of the etching solution gradually decreased, leading to a gradual decrease in the silicon oxide etching rate to a negative value; while the oxygen sacrificial agent in the examples continuously consumed the active oxygen in the etching solution, preventing the organic amine from being oxidized, improving stability, and thus maintaining a stable etching rate.
[0039] Table 3 shows the etching rates of silicon oxide after dissolving silicic acid in some examples and comparative examples. Comparative Example 4 is a high-selectivity silicon nitride etchant based on phosphoric acid. Although the silicon nitride etching rate is relatively high, the silicon oxide etching rate drops to -15.76 Å / 30 min when the Si concentration is increased to 1000 ppm. In contrast, the silicon oxide etching rate in each example and Comparative Example 1 decreases slowly with increasing Si concentration, and the silicon oxide etching rate is still greater than 0.2 Å / 30 min at a Si concentration of 4000 ppm. This demonstrates that silicic acid has a relatively small effect on the silicon oxide etching rate in alkaline systems and has a significant advantage in etching ultra-high aspect ratio structures.
[0040] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.
Claims
1. A selective etching solution for silicon nitride and silicon oxide, characterized in that: By mass fraction, it includes 60-70% tris(2-aminoethyl)amine, 1.0-2.0% silicon oxide etching inhibitor, 4.0-5.0% silane dispersant, 0.2-0.3% etching stabilizer, 0.1-0.2% oxygen sacrificial agent, and the balance being deionized water.
2. The selective etching solution for silicon nitride and silicon oxide according to claim 1, characterized in that: The silicon oxide etching inhibitor is one of propyltrimethoxysilane, isopropyltrimethoxysilane, n-butyltrimethoxysilane, isobutyltrimethoxysilane, and tert-butyltrimethoxysilane.
3. The selective etching solution for silicon nitride and silicon oxide according to claim 1, characterized in that: The silane dispersant is one of n-propanol, isopropanol, n-butanol, isobutanol, and tert-butanol.
4. The selective etching solution for silicon nitride and silicon oxide according to claim 1, characterized in that: The etching stabilizer is one of polyvinyl alcohol, polyethylene glycol 2000, Triton X-100, and Tween 80.
5. The selective etching solution for silicon nitride and silicon oxide according to claim 1, characterized in that: The oxygen sacrificial agent is one of ascorbic acid, methyl ethyl ketone oxime, gallic acid, and tert-butylhydroquinone.
6. The selective etching solution for silicon nitride and silicon oxide according to claim 1, characterized in that: The etching temperature of the etching solution is 105-120℃.
7. The selective etching solution for silicon nitride and silicon oxide according to claim 1, characterized in that: The etching solution has an etching selectivity ratio of >600 for silicon nitride and silicon oxide.
8. The selective etching solution for silicon nitride and silicon oxide according to claim 1, characterized in that: The etching solution has an etching rate of >16 Å / min for SiN.
9. A method for preparing the selective etching solution of silicon nitride / silicon oxide according to any one of claims 1-8, characterized in that: Includes the following steps: First, prepare a (2-aminoethyl)amine solution. Then, add an oxygen sacrificial agent, a silane dispersant, an etching stabilizer, and a silicon oxide etching inhibitor to the tri(2-aminoethyl)amine solution in sequence. Stir until the etching solution is colorless and transparent to obtain the etching solution.
10. The use of the selective etchant of silicon nitride / silicon oxide according to any one of claims 1-8 in etching semiconductor materials containing silicon nitride and silicon oxide.