Water-containing acid etching solution and preparation method thereof

Abstract

The invention discloses a water-containing acid etching solution and a preparation method thereof, the water-containing acid etching solution comprises acid, ammonium fluoride and a surfactant with the molecular formula of # imgabs0 #, Rf is a long-chain alkyl group, N is nitrogen, R1, R2 and R3 are respectively any one of H or short-chain alkyl groups below C4, and M <-> is anions, and tests show that the water-containing acid etching solution has the advantages that due to the fact that the surfactant with the molecular formula of # imgabs1 # is added, the water-containing acid etching solution can be used for preparing the water-containing acid etching solution; the surface tension of the solution is obviously reduced, compared with a buffer oxide etching solution without adding the surfactant, the surface tension is lower, the etching rate is not greatly changed, the contact angle is also obviously reduced, and the content of particles in the product is not increased by the surfactant, so that the solution can be stored by standing for a long time; and the properties cannot be changed in some extreme environments, and the performance is excellent.

Description

Technical Field

[0001] The present invention relates to the technical field of BOE buffered oxide etchant, and specifically to an aqueous acid etching solution and a preparation method thereof. Background Art

[0002] With the rapid advancement of the digital and intelligent era, semiconductors, as a member of the core technologies, have shown a continuous upward trend in market demand. Specifically, in many fields such as 5G communication, cloud computing, and data centers, the demand for high-performance, high-speed, and highly integrated semiconductor chips is extremely strong, which has strongly promoted the development of the semiconductor market. In addition, the gradual recovery of the global economy has effectively driven the consumer demand for electronic products, thus further increasing the demand for semiconductor products. Using wet etching to precisely control the micro-scale patterns of chips has become an important process in chip production.

[0003] The existing BOE (Buffered Oxide Etch), buffered oxide etchant is formed by mixing hydrofluoric acid with water or ammonium fluoride with water, and is a key wet etchant, which is commonly used for etching silicon dioxide (SiO2) and silicon nitride (Si3N4) films. The BOE stock solution mainly contains hydrofluoric acid (HF) and ammonium fluoride (NH4F), and also a surfactant. HF is the main etchant, and NH4F is used as a buffer. Using NH4F to fix the concentration of [H + , so as to maintain a certain etching rate. Among them, the surfactant has been increasingly widely used in the microelectronics industry with its unique characteristics of reducing surface tension, dispersing and suspending, and wetting and penetrating. Especially its application in the slicing, grinding, polishing, and cleaning processes of silicon materials has become an essential auxiliary material for reducing damage, defects, and contamination.

[0004] However, the current BOE buffered oxide etchant has too high surface tension and too large contact angle of the liquid with the solid surface, resulting in poor performance of the BOE buffered oxide etchant. Summary of the Invention

[0005] The purpose of the present invention is to provide an aqueous acid etching solution to solve the defects in the above background art.

[0006] To achieve the above purpose, the present invention provides the following technical solution: An aqueous acid etching solution, comprising: an acid, ammonium fluoride, and a surfactant with the molecular formula wherein, Rf is a long-chain alkyl group, N is nitrogen, R1, R2, and R3 are each any one of H or short-chain alkyls with 4 or less carbon atoms, and M - is an anion.

[0007] This aqueous acid etching solution, due to the addition of the surfactant with the molecular formula The surfactant significantly reduces the surface tension of the solution. Compared with the buffered oxide etchant without the surfactant, it has a lower surface tension, and the etching rate does not change significantly. Moreover, the contact angle also decreases significantly, and the surfactant does not increase the particles in the product, enabling the solution to be stored statically for a long time and its properties not to change in some extreme environments, with excellent performance.

[0008] Preferably, Rf is C 12 H 25 , M - is Cl - , R1, R2 and R3 are all CH3, and the molecular formula is C 12 H 25 N(CH3)3Cl.

[0009] Preferably, Rf is C 16 H 33 , M - is Cl - , R1, R2 and R3 are all CH3, and the molecular formula is C 16 H 33 N(CH3)3Cl.

[0010] Preferably, Rf is C 18 H 37 , M - is Cl - , R1, R2 and R3 are all CH3, and the molecular formula is C 18 H 37 N(CH3)3Cl.

[0011] Preferably, the acid is selected from one or more of sulfuric acid, hydrochloric acid, nitric acid, and hydrofluoric acid.

[0012] Preferably, the acid is hydrofluoric acid, the concentration of hydrofluoric acid in the solution is 0 - 20%, and the concentration of ammonium fluoride is 0 - 40%.

[0013] This application also provides a preparation method of an aqueous acid etchant solution for preparing the aqueous acid etchant solution described above, including:

[0014] S1: Using an industrial-grade finished surfactant, adding a salting-out reagent to extract metal impurities in the surfactant, so that the metal impurities are extracted into the salting-out reagent to reduce the metal impurity content of the surfactant;

[0015] S2: After removing the metal impurities, the salting-out reagent is removed by heating and distillation to obtain a high-purity surfactant;

[0016] S3: Detect the content of metal impurities in the surfactant before and after purification. If it meets the standard, it is used to prepare the aqueous acid etching solution. If it does not meet the standard, repeat the above steps S1 and S2 to continue removing metal impurities until the metal impurity content meets the standard;

[0017] S4: Mix the surfactant with a qualified metal impurity content with acid, ammonium fluoride and water in proportion to obtain the aqueous acid etching solution.

[0018] Preferably, the salting-out reagent is electronic-grade ammonia water.

[0019] Compared with the prior art, the beneficial effect of the present invention is that: due to the addition of a surfactant with the molecular formula in this aqueous acid etching solution, the surface tension of the solution is significantly reduced. Compared with the buffered oxide etchant without the surfactant added, it has a lower surface tension, and the etching rate does not change significantly, and the contact angle is also significantly reduced. Moreover, the surfactant does not increase the particles in the product, enabling the solution to be stored statically for a long time and its properties will not change under some extreme environments, with excellent performance. Specific Embodiments

[0020] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0021] Embodiment 1

[0022] The present invention provides an aqueous acid etching solution, including: acid, ammonium fluoride, and a surfactant with the molecular formula wherein, Rf is a long-chain alkyl group, N is nitrogen, R1, R2, and R3 are each any one of H or short-chain alkyls with 4 or fewer carbons, and M - is an anion. The surfactant can be one or more of dodecyltrimethylammonium chloride, cetyltrimethylammonium chloride, or octadecyltrimethylammonium chloride. The solution also contains hydrofluoric acid and ammonium fluoride, wherein the concentration of hydrofluoric acid is 0-20%, and the concentration of ammonium fluoride is 0-40%.

[0023] Embodiment 2

[0024] The present invention provides a preparation method for an aqueous acid etching solution, including:

[0025] S1: Use an industrial-grade finished surfactant, add a salting-out reagent to extract the metal impurities in the surfactant, so that the metal impurities are extracted into the salting-out reagent to reduce the metal impurity content of the surfactant;

[0026] S2: After removing metal impurities, the salting-out reagent is removed by heating and distillation to obtain a surfactant with high purity.

[0027] S3: Detect the metal impurity content in the surfactant before and after purification. If it meets the standard, it is used to prepare an aqueous acid etchant solution. If it does not meet the standard, repeat the above steps S1 and S2 to continue removing metal impurities until the metal impurity content meets the standard.

[0028] S4: Mix the surfactant with a qualified metal impurity content, acid, ammonium fluoride and water in proportion to obtain an aqueous acid etchant solution.

[0029] 8. The preparation method of an aqueous acid etchant solution according to claim 7, wherein the salting-out reagent is electronic-grade ammonia water.

[0030] Example 3

[0031] In this example, the purchased industrial-grade finished product dodecyltrimethylammonium chloride is used. Due to the excessive metal impurities, the method of Example 2 is adopted for treatment and preparation of the aqueous acid etchant solution. We use electronic-grade ammonia water for salting out to reduce its metal impurities, and then remove the ammonia water by heating and distillation to obtain a surfactant with higher purity. Then, the metal impurity content in the surfactant before and after purification is detected as shown in the following table.

[0032]

[0033] , the unit in the table is ppt. After detection, the metal impurity content meets the standard. Then, the surfactant with a qualified metal impurity content, acid, ammonium fluoride and water are mixed in proportion to obtain an aqueous acid etchant solution. Then, the surface tension and contact angle of the aqueous acid etchant solution are measured. In this example, dodecyltrimethylammonium chloride is used. This surfactant is relatively stable in the buffered oxide etchant solution, and its main function is to reduce the surface tension of the solution. Compared with the buffered oxide etchant solution without adding surfactant, it has a lower surface tension, and the etching rate does not change significantly, and the contact angle also decreases significantly. The purified surfactant will not increase the particles in the product, and its properties will not change even after long-term static storage, and even in some extreme environments.

[0034] Moreover, according to the substrate used and the magnitude of the etching rate, the concentration of the buffered oxide etchant solution can be adjusted. The concentration of hydrofluoric acid can vary between 0-20%, and the concentration range of ammonium fluoride is between 0-40%. The magnitude of the concentration also depends on the storage environment. A high concentration is likely to crystallize at low temperature and affect the performance.

[0035] The methods for measuring surface tension and contact angle are as follows: All surface tensions are measured using a DY-300 surface tensiometer, and the Wilhelmy (platinum plate method) is used for measurement. For the contact angle, a DMO-501 is used. After adding a surfactant (usually, the intermolecular forces between surfactant molecules are very weak), it automatically accumulates on the surface, which weakens the intermolecular interactions in the surface layer, reduces the surface tension of the solution, and further reduces the surface Gibbs function. The more the Gibbs function decreases, the easier it is to wet. It can also be expressed as the surface of the solution becoming more extended, the contact area of the liquid with the solid surface increasing, and the wetting angle increasing, making it easier to be wetted.

[0036] The measurement results of surface tension and contact angle are shown in the following table:

[0037] Sample Name Surface Tension (mN / m) BOE without Surfactant 90.3 BOE with Surfactant 37.3

[0039] Sample Name Contact Angle (°) BOE without Surfactant 83.2 BOE with Surfactant 52.0

[0040] It was found through measurement that the surface tension and contact angle of the aqueous acid etching solution in this example are significantly smaller than those without adding dodecyl trimethyl ammonium chloride.

[0041] Finally, the etching rate of the aqueous acid etching solution in this example was measured, including: A film thickness measuring instrument ST5030-SL was used for the film thickness machine. BOE (HF: 1.6%, NH4F: 38.9%) was selected, the etching temperature was 20.0 °C, the etching time was 5 min, and the selected wafer was SiO2. The test results are shown in the following table:

[0042] Sample Name E.R. (nm / min) BOE without Surfactant 19.3 BOE with Surfactant 19.3

[0043] It can be seen that the addition of dodecyl trimethyl ammonium chloride does not affect the etching rate.

[0044] It should be noted that by adjusting the contents of cetyl trimethyl ammonium chloride and octadecyl trimethyl ammonium chloride, the same effect as that of dodecyl trimethyl ammonium chloride can be achieved.

[0045] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be encompassed within the present invention. Any reference signs in the claims should not be regarded as limiting the claimed rights.

Claims

1. An aqueous acid etching solution, characterized in that, Comprising: An acid, ammonium fluoride, and a surfactant having the molecular formula , where Rf is a long-chain alkyl group, N is nitrogen, R1, R2, and R3 are each independently either H or a short-chain alkyl group having 4 or fewer carbon atoms, and M - is an anion.

2. The aqueous acid etching solution according to claim 1, wherein Rf is C 12 H 25 , M - is Cl - , R1, R2 and R3 are all CH3, and the molecular formula is C 12 H 25 N(CH3)3Cl.

3. An aqueous acid etching solution according to claim 1, wherein, The Rf is C 16 H 33 , M - is Cl - , R1, R2 and R3 are all CH3, and the molecular formula is C 16 H 33 N(CH3)3Cl.

4. An aqueous acid etching solution according to claim 1, characterized in that, The Rf is C 18 H 37 , M - is Cl - , R1, R2 and R3 are all CH3, and the molecular formula is C 18 H 37 N(CH3)3Cl 5. An aqueous acid etching solution according to claim 1, wherein, The acid is selected from one or more of sulfuric acid, hydrochloric acid, nitric acid, and hydrofluoric acid.

6. An aqueous acid etching solution according to claim 5, wherein, The acid is hydrofluoric acid, and the concentration of hydrofluoric acid in the solution is 0-20%, and the concentration of ammonium fluoride is 0-40%.

7. A method for preparing an aqueous acid etching solution for preparing the aqueous acid etching solution according to any one of claims 1-6, characterized in that, Comprising: S1: Using an industrial-grade finished surfactant, adding a salting-out reagent to extract metal impurities in the surfactant, so that the metal impurities are extracted into the salting-out reagent to reduce the metal impurity content of the surfactant; S2: After removing the metal impurities, the salting-out reagent is removed by heating and distillation to obtain a high-purity surfactant; S3: Detect the metal impurity content in the surfactant before and after purification. If it meets the standard, it is used to prepare an aqueous acid etching solution. If it does not meet the standard, repeat the above steps S1 and S2 to continue removing metal impurities until the metal impurity content meets the standard; S4: Mix the surfactant with a qualified metal impurity content, acid, ammonium fluoride, and water in proportion to obtain an aqueous acid etching solution.

8. A method for preparing an aqueous acid etching solution according to claim 7, characterized in that, The salting-out reagent is electronic-grade ammonia water.

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