Selective etching solution for molybdenum and tungsten
By optimizing the ratio of electronic grade phosphoric acid, acetic acid and amine salt buffers in the etching liquid, and adding surfactant and tungsten etch inhibitors, high selective ratio selective etching of molybdenum and tungsten is achieved, solving the problem of difficult selective etching of molybdenum and tungsten in the prior art, and improving the etching efficiency and surface quality.
Patent Information
- Application Number
- CN202411763113.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-03
- Publication Date
- 2025-04-11
AI Technical Summary
In 3D NAND flash technology, molybdenum (Mo) and tungsten (W) often co-exist in the same structure, resulting in increased selective etching difficulty. Especially in scenarios where tungsten is required to retain and remove molybdenum, it is difficult for the prior art to achieve efficient and accurate selective etching.
A selective etching solution of molybdenum and tungsten is provided, which consists of 50%-63% electronic grade phosphoric acid, 10%-15% electronic grade acetic acid, 0.8%-3% oxidant, 0.5%-4% amine salt buffer, 0.06%-1.5% surfactant and 0.3%-1.5% tungsten etching inhibitor, and the rest is deionized water. This etching solution ensures that the etching rate of molybdenum is high and the tungsten etching rate is low by optimizing the ratio of acidic substances and buffers, and achieves a high selection ratio of molybdenum and tungsten.
A high selection ratio between molybdenum and tungsten is achieved, ensuring that the etching rate of molybdenum reaches above 6.25nm/min, while the etching rate of tungsten remains below 0.195nm/min, improving the controllability and surface quality of the etching process.
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Abstract
Description
Technical Field
[0001] The invention belongs to the field of electronic chemicals, and in particular relates to a selective etching solution for molybdenum and tungsten. Background Art
[0002] The emergence of 3D NAND flash memory technology marks a major advancement in memory technology. Compared with the traditional 2D NAND structure, 3D NAND stacks multiple memory cell layers in the vertical direction, greatly increasing storage density and performance. This technological innovation requires the use of a series of complex materials and processes in the manufacturing process, among which molybdenum (Mo) and tungsten (W) are widely used in metal interconnects and control gates of 3D NAND devices due to their excellent electrical and mechanical properties.
[0003] Molybdenum (Mo) and tungsten (W) are two important transition metals that are widely used in semiconductor manufacturing, microelectronic devices and optical devices due to their excellent conductivity, thermal stability and mechanical properties. However, in practical applications, molybdenum and tungsten often coexist in the same structure, so how to achieve selective etching of them has become a key technical challenge. Especially in the scenario where tungsten needs to be retained and molybdenum needs to be removed, it is particularly important to develop an efficient and accurate selective etching solution. Summary of the invention
[0004] In order to solve the above problems, the present invention aims to provide a selective etching solution for molybdenum and tungsten, which ensures that the etching rate of metal tungsten is low and molybdenum is etched faster, while ensuring that molybdenum and tungsten have a higher selectivity, and ensures that molybdenum and tungsten have a higher selectivity under the premise of ensuring that molybdenum ER≥6.25nm / min and tungsten ER≤0.195nm / min.
[0005] The technical solution of the present invention is as follows: A selective etching solution for molybdenum and tungsten, the etching solution comprising the following components by mass fraction: 50%-63% electronic grade phosphoric acid, 10%-15% electronic grade acetic acid, 0.8%-3% oxidant, 0.5%-4% amine salt buffer, 0.06%-1.5% surfactant, 0.3%-1.5% tungsten etching inhibitor, and the rest is deionized water.
[0006] Preferably, the phosphoric acid is electronic grade, with a raw material concentration of ≥85% and a metal ion content of ≤0.02ppm; Acetic acid is electronic grade, raw material concentration ≥99%, metal ion content ≤0.02ppm; The oxidant is one of nitric acid aqueous solution, hydrogen peroxide, perchloric acid aqueous solution, and peracetic acid aqueous solution, preferably nitric acid aqueous solution; the amine salt buffer is one or more of N-methyl-2-pyrrolidone, aminomethyl propanol, triethanolamine, and pyrrolidine.
[0007] Preferably, the etching solution further comprises the following components by mass fraction: 0.05%-0.45% of a roughness regulator.
[0008] More preferably, the roughness regulator is 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid or N,N-bis(2-hydroxyethyl)glycine.
[0009] More preferably, the etching solution further comprises the following components in terms of mass fraction: 0.08%-1.5% of a roughness inhibitor; Still more preferably, the roughness inhibitor is one or more of bile acid, catechin, cyclodextrin, and sucrose monoester. Preferably, the surfactant is a nonionic surfactant, specifically one or more of nonylphenol polyoxyethylene ether, benzotriazole, Tween-20, polyethylene glycol octylphenyl ether, and nonylphenol polyethoxylate ether. Preferably, the tungsten etching inhibitor is one or more of 2-mercaptobenzothiazole, 2-octyl imidazoline, mercaptobenzimidazole, polyoxyethylene stearate, and dihydroxymethyl dihydroxyethylene urea. The above tungsten etching inhibitor can be adsorbed on the tungsten surface, increase the contact resistance between the etching solution and the tungsten surface, slow down the etching rate, make the etching process more controllable, and reduce the defects and non-uniformity that may occur during the etching process, and improve the surface quality and structural integrity after etching.
[0010] Preferably, the ER of molybdenum is ≥6.25nm / min, and the ER of tungsten is ≤0.195nm / min.
[0011] Preferably, the etching solution is used at a temperature ranging from 20°C to 60°C, preferably 40°C.
[0012] Compared with the prior art, the advantages of the present invention are: 1. Phosphoric acid, the main acid substance used in the etching solution, has a good selective etching effect on molybdenum.
[0013] 2. The introduced amine salt buffer can help maintain the pH value of the etching solution within a stable range, thereby improving the selectivity of molybdenum and tungsten.
[0014] 3. The introduced roughness regulator and inhibitor can effectively inhibit the increase of surface roughness during etching, thereby improving the smoothness of the chip surface.
[0015] 4. Non-ionic surfactants cannot dissolve into ions in aqueous solution and have high stability. In addition, they can reduce the surface tension of the etching solution, improve the uniformity and consistency of etching, and can be adsorbed on the surface of tungsten to slow down its etching rate and improve the selectivity of molybdenum and tungsten.
[0016] 5. The introduced tungsten etching inhibitor can be adsorbed on the tungsten surface, increase the contact resistance between the etching solution and the tungsten surface, slow down the etching rate, make the etching process more controllable, and at the same time reduce the defects and unevenness that may occur during the etching process, and improve the surface quality and structural integrity after etching. DETAILED DESCRIPTION
[0017] 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.
[0018] In the context of this specification, except for the contents explicitly described, any matters or items not mentioned directly use the technology known in the art. Moreover, any embodiment described in this patent can be freely combined with one or more other embodiments described in this patent, and the technical solutions or technical ideas formed thereby are regarded as part of the original disclosure or original record of the present invention, and should not be regarded as new content not disclosed in this patent, unless a person skilled in the art considers that the combination is obviously unreasonable.
[0019] The data points disclosed in the present invention include not only the specifically disclosed numerical points, but also the endpoints of each numerical range. Any combination of these data points should be regarded as the disclosed or recorded range of the present invention, regardless of whether these numerical points are disclosed one by one in this article. The percentages in the following examples and comparative examples are all by mass. The reagents are all 99% pure; water is deionized water Examples 1-12 and Comparative Examples 1-6 The present invention is further described below in conjunction with specific examples 1-12 and comparative examples 1-6. The present invention is further described in detail, but is not limited to these examples, as shown in Table 1-2. Table 1
[0020] Table 2 Etching experiment The etching experiments were carried out using the etching solutions described in the above embodiments and comparative examples, respectively. The specific operation process is as follows: 100g of etching solution is prepared according to the above different formulas, placed in a round-bottom three-hole flask with a volume of 100ml, and a stirrer is added to the flask. The temperature of the electric heating pot is set to 40°C, and the stirring rate is 100r / min. When the solution temperature reaches and stabilizes at 40±0.5°C, the molybdenum monolith is etched (thickness is about 45nm). Before etching, the molybdenum monolith is cut into 2*1cm test pieces, and its initial thickness is tested using four probes, measured four times, and the arithmetic mean is taken. Next, the test piece is placed in the etching solution and etched for 5min, rinsed with clean water, and blown dry with nitrogen. The thickness of the test piece after etching is tested using four probes, measured twice, and the arithmetic mean is taken. The molybdenum etching rate is obtained by calculation.
[0021] Similarly, 100g of etching solution is prepared according to the above different formulas, placed in a round-bottom three-hole flask with a volume of 100ml, and a stirrer is added to the flask, the temperature of the electric heating pot is set to 40°C, the stirring rate is 100r / min, and when the solution temperature reaches and stabilizes at 40±0.5°C, the tungsten sheet is etched (its thickness is about 80nm). Before etching, the tungsten sheet is cut into regular square test pieces of 2*2cm. In order to avoid the influence of the oxide layer on the surface of the tungsten sheet on the experimental results, the tungsten sheet is rinsed with clean water in advance and then blown dry with nitrogen. Use four probes to test its initial thickness, measure four times, and take the arithmetic mean. Put the tungsten sheet into the etching solution for 30min, rinse it with clean water, and blow it dry with nitrogen. Use four probes to measure the thickness of the test piece after etching, measure four times, and take the arithmetic mean. The etching rate of metal tungsten is obtained by calculation. The experimental results of all embodiments and comparative examples are shown in Table 3 below.
[0022] Table 3 Experimental results
[0023] From the experimental data and the selectivity values in Table 3, it can be seen that, compared with Example 8, Comparative Examples 1 and 2 only use electronic grade phosphoric acid with a mass content of 60% and acetic acid with a mass content of 12% as etching solutions, and the etching rates of molybdenum and tungsten are very low. Compared with Example 8, no oxidant is added in Comparative Example 3, and the etching rate of molybdenum is low, and the etching effect on tungsten is small. The presence of the oxidant can increase the activity of the molybdenum surface through oxidation, making it easier to be dissolved by the components in the etching solution; Compared with Example 8, no amine salt buffer is added in Comparative Example 4, the etching rate of tungsten is accelerated, and the selectivity of molybdenum and metal tungsten is reduced. Compared with Example 8, no surfactant is added to the etching solution in Comparative Example 5, the etching rate of molybdenum does not change much, the etching rate of metal tungsten is accelerated, and the selectivity of molybdenum and metal tungsten is reduced. The surfactant can be preferentially adsorbed on the surface of tungsten, slowing down its etching rate, thereby increasing the selectivity of molybdenum and tungsten. Compared with Example 8, no metal tungsten etching inhibitor is added in Comparative Example 6, and the etching rate of metal tungsten element is significantly accelerated, resulting in a decrease in the selectivity of molybdenum and tungsten. Tungsten etching inhibitors can be adsorbed on the tungsten surface, increase the contact resistance between the etching solution and the tungsten surface, slow down the etching rate, and make the etching process more controllable. Compared with Example 8, Examples 13 and 14 did not add roughness regulators and inhibitors, respectively, and their surface roughness increased significantly. This may be because the ring structure and hydroxyl groups in the structure of the roughness inhibitor can interact with the active ingredients in the etching solution, stabilize its chemical properties, and inhibit the side effects that may occur during the etching process, thereby reducing the surface roughness; and the ammonium ions in the roughness regulator can be adsorbed on the surface of the material, complex with the metal ions in the solution, stabilize the chemical state of the solution, reduce the phenomenon of local over-etching, and smooth the surface. The synergistic effect of these two additives can effectively improve the surface treatment effect during the etching process and make the surface finish higher after etching.
[0024] The technical solution of the present invention is explained through the above embodiments, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above specific embodiments to be implemented. Any improvements made by technicians in the relevant field based on the present invention, or equivalent replacement of the materials selected by the present invention, etc., fall within the scope of protection of the patent.
Claims
1. A selective etching solution for molybdenum and tungsten, characterized in that: The etching solution comprises the following components by mass fraction: 50%-63% electronic grade phosphoric acid, 10%-15% electronic grade acetic acid, 0.8%-3% oxidant, 0.5%-4% amine salt buffer, 0.06%-1.5% surfactant, 0.3%-1.5% tungsten etching inhibitor, and the rest is deionized water.
2. The selective etching solution for molybdenum and tungsten according to claim 1, characterized in that: The phosphoric acid is electronic grade, with a raw material concentration of ≥85% and a metal ion content of ≤0.02ppm; Acetic acid is electronic grade, with raw material concentration ≥99% and metal ion content ≤0.02ppm.
3. The selective etching solution for molybdenum and tungsten according to claim 1, characterized in that: The oxidant is one of nitric acid aqueous solution, hydrogen peroxide, perchloric acid aqueous solution, and peracetic acid aqueous solution, preferably nitric acid aqueous solution; The amine salt buffer is one or more of N-methyl-2-pyrrolidone, aminomethyl propanol, triethanolamine and pyrrolidine.
4. The selective etching solution for molybdenum and tungsten according to claim 1, characterized in that: The etching solution also includes the following components by mass fraction: 0.05%-0.45% roughness conditioner.
5. The selective etching solution for molybdenum and tungsten according to claim 4, characterized in that: The roughness regulator is 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid and N,N-bis(2-hydroxyethyl)glycine.
6. The selective etching solution for molybdenum and tungsten according to claim 5, characterized in that: The etching solution also includes the following components by mass fraction: 0.08%-1.5% roughness inhibitor; preferably, the roughness inhibitor is one or more of bile acid, catechin, cyclodextrin, and sucrose monoester.
7. The selective etching solution for molybdenum and tungsten according to claim 1, characterized in that: The surfactant is a nonionic surfactant, specifically one or more of nonylphenol polyoxyethylene ether, benzotriazole, Tween-20, polyethylene glycol octylphenyl ether, and nonylphenol polyethoxylate ether.
8. The selective etching solution for molybdenum and tungsten according to claim 1, characterized in that: The tungsten etching inhibitor is one or more of 2-mercaptobenzothiazole, 2-octyl imidazoline, mercaptobenzimidazole, polyoxyethylene stearate, and dihydroxymethyl dihydroxyethylene urea.
9. The selective etching solution for molybdenum and tungsten according to claim 1, characterized in that: The ER of molybdenum is ≥6.25nm / min, and the ER of tungsten is ≤0.195nm / min.
10. The selective etching solution for molybdenum and tungsten according to claim 1, characterized in that: The use temperature range of the etching solution is 20°C-60°C, preferably 40°C.