An etching solution for producing car-grade silicon nitride chips and a method of using the same

Abstract

The application discloses a kind of etching liquid in the field of etching liquid, by weight, containing hydrogen fluoride 6-9%, butanedinitrile 5-8%, ethanol 15-20%, and the balance is ultrapure water.The complexation reaction of butanedinitrile and hydrofluoric acid can be prevented in the application, and the hydrolysis of hydrofluoric acid is prevented.The complex can be gradually dissociated by temperature control, so that the effective concentration of hydrofluoric acid in the solution can be maintained, and there is no need to frequently supplement hydrofluoric acid into the solution or constantly prepare new hydrofluoric acid solution, and there is no need to use other surfactants.The etching liquid has the advantages of long-acting, stable and low cost, and can be used in the etching processing of vehicle-grade silicon nitride chip.

Description

Technical Field

[0001] This invention relates to an etching solution, and more particularly to an etching solution used in the production of silicon nitride chips. Background Technology

[0002] Silicon nitride (SiN) chips are produced using low-pressure chemical vapor deposition (LPCVD) technology. A high-quality SiN film is grown on a silicon substrate, and the desired optical structures are etched onto this film. Finally, excess SiN and silicon layers are removed by etching, resulting in a suspended SiN chip.

[0003] In the manufacturing process of silicon nitride chips, etching solutions are widely used in various process steps. Various structures of silicon nitride chips can be formed through liquid etching. The main applications of etching solutions in the silicon nitride chip manufacturing process are:

[0004] 1. Forming Circuits and Components: In the early stages of silicon nitride chip manufacturing, etching solutions were used to form circuits and components. Through techniques such as photolithography and development, the patterns of circuits and components are transferred onto the semiconductor material, and then etching solutions are used to transfer the patterns onto the semiconductor material, thus forming the circuits and components.

[0005] 2. Chip Dividing: In the manufacturing of silicon nitride chips, it is typically necessary to divide the semiconductor chip into individual chips. This process can be achieved using anisotropic etching solutions. By controlling parameters such as the concentration, temperature, and processing time of the etching solution, specific areas on the chip can be removed, thereby dividing it into individual chips.

[0006] 3. Deburring and Cleaning: Deburring and cleaning processes may be required at various stages of silicon nitride chip manufacturing. This process can be achieved using etching solutions containing acids or alkalis. These etching solutions remove edge burrs and surface contaminants, resulting in a smoother and cleaner surface.

[0007] A selective etching solution for silicon oxide is disclosed in the Chinese Patent Database, publication number CN115181569A, publication date: 20221014. The etching solution comprises 0.1-5 wt% hydrofluoric acid, 10-30 wt% ammonium fluoride, 0.01-0.2 wt% amide inhibitors, 0.005-0.1 wt% amino alcohol additives, and the balance being ultrapure water. The amide inhibitors are one or more of 2-aminopropionamide, 2-aminobutyramide, 2-amino-2,3-dimethylbutyramide, 3-aminopropionamide, 3-(methylamino)propionamide, and 3-(propylamino)propionamide. The additive is one or more of 2-amino-n-butanol, 4-amino-2-butanol, 2-amino-3-methyl-1-butanol, 4-amino-1-butanol, 3-diethylamino-1-propanol, 5-amino-2,2-dimethylpentanol, and D-aminopropanol.

[0008] Its shortcomings are:

[0009] 1. Existing chip etching solutions have complex compositions, are difficult to formulate, and are costly.

[0010] 2. Most chip etching solutions contain hydrofluoric acid. When the amount of hydrofluoric acid is too high, it reacts violently with silicon or silicon dioxide, making it difficult to control the etching amount. Therefore, the weight content of hydrofluoric acid is usually controlled at a low level. However, during the etching process, the concentration of hydrofluoric acid will drop rapidly. Therefore, it is necessary to continuously add hydrofluoric acid to the etching solution, resulting in frequent etching solution replacements and complicated operation.

[0011] 3. Currently, the manufacturing of automotive-grade silicon nitride chips requires high reliability. During manufacturing, it is necessary to ensure etching precision, cut quality, and etching stability. The etching rate is usually selected as 30-80 μm / min, at which other parameters are easier to control. However, existing etching solutions are difficult to meet such production requirements. Summary of the Invention

[0012] The purpose of this invention is to provide an etching solution for automotive-grade silicon nitride chip production, which eliminates the need for frequent replenishment of hydrofluoric acid during chip etching. Instead, temperature control is sufficient to maintain the effective concentration of hydrofluoric acid in the solution at a suitable etching concentration.

[0013] The objective of this invention is achieved as follows: An etching solution for the production of automotive-grade silicon nitride chips, by weight containing 6-9% hydrogen fluoride, 5-8% succinic anion, 15-20% ethanol, and the balance being ultrapure water.

[0014] Furthermore, the etching solution is prepared by first passing hydrogen fluoride gas into ultrapure water at 15-25°C, then adding succinate and ethanol, and stirring for 10-30 minutes.

[0015] The present invention provides a method for using an etching solution for the production of automotive-grade silicon nitride chips, which involves using the etching solution to etch silicon oxide layers and silicon layers.

[0016] The etching solution is used in an environment of 40-65℃ during etching. The etching solution is preheated to 40℃ before etching, and then the temperature is increased according to the hydrogen fluoride consumption rate during the etching process to keep the H ion concentration in the solution constant.

[0017] The etching solution can be used not only to divide semiconductor chips into individual chips, but also to etch silicon wafers to form silicon nitride chip circuits and components.

[0018] In this invention, succinic anhydride can undergo a complexation reaction with hydrofluoric acid, preventing the hydrolysis of hydrofluoric acid. Furthermore, by controlling the temperature, the complex can be gradually dissociated, thus maintaining an effective concentration of hydrofluoric acid in the solution. This eliminates the need for frequent replenishment of hydrofluoric acid or continuous preparation of new hydrofluoric acid solutions, and also eliminates the need for other surfactants. Ethanol, as a volatile carrier, helps to remove the SiF4 and NH3 gases generated during the etching process via a vacuum device. This etching solution offers advantages such as long-lasting effectiveness, stability, and low cost, making it suitable for etching automotive-grade silicon nitride chips. Detailed Implementation

[0019] Example 1

[0020] An etching solution for the production of automotive-grade silicon nitride chips contains, by weight, 80 grams of hydrogen fluoride, 60 grams of succinic anionylene, 200 grams of ethanol and 660 grams of ultrapure water.

[0021] When preparing the etching solution, hydrogen fluoride gas is first introduced into ultrapure water at 15-25℃. Hydrogen fluoride gas and water are infinitely miscible. Then, succinate and ethanol are added and stirred for 10-30 minutes to obtain the solution.

[0022] The etching solution is used to etch silicon nitride and silicon layers. During etching, SiF4 gas and NH3 are generated, which can be extracted by vacuuming.

[0023] The etching solution is used in an environment of 40-65℃. The etching solution is preheated to 40℃ before etching, and then the temperature is increased according to the consumption rate of hydrogen fluoride during the etching process to keep the H ion concentration in the solution constant.

[0024] This etching solution can be used not only to divide semiconductor chips into individual chips, but also to etch silicon wafers to form silicon nitride chip circuits and components.

[0025] In the etching solution formulation of Example 1, hydrogen fluoride and succinic acid can form succinic acid complex hydrofluoric acid at room temperature, and the reaction can be represented by the following equation:

[0026] C4H5N+HF→C4H5N·HF

[0027] The mechanism of this complexation reaction is as follows: First, the nitrogen atom in succinate forms a nucleophilic bond with the hydrogen atom in HF through its lone pair electrons. Second, after the nucleophilic attack, the nitrogen atom in succinate forms a coordinate bond with the hydrogen atom in HF, forming a succinate-HF complex. Third, charge rearrangement occurs; after the formation of the coordinate bond, the electron cloud rearrangement allows for a better distribution of the positive charge on the nitrogen atom, enhancing the stability of the complex.

[0028] The molar ratio of succinate to hydrofluoric acid in the complexation reaction is approximately 1:1. Excess hydrofluoric acid remains in a free state within the system and hydrolyzes to form an acidic solution. This complexation reaction can proceed at 15-25°C. The applicant's research has revealed that the dissociation temperature of this complex is not high, and the coordinating ion's coordination ability is relatively weak. It gradually dissociates between 35-85°C, and almost completely dissociates at 85°C. This allows for temperature control to maintain the effective concentration of hydrofluoric acid in the solution.

[0029] Ethanol, as a volatile carrier, can help separate the SiF4 gas generated during the etching process and remove it through a vacuum device. Furthermore, ethanol, as an organic solvent, can clean organic matter from the wafer surface.

[0030] Example 2

[0031] Based on Comparative Document 1, the amount of hydrogen fluoride was screened, i.e., using hydrogen fluoride as a single variable, etching solutions with different HF contents were prepared. The etching solutions were used to wet etch silicon nitride wafers at 50°C to etch trapezoidal grooves on the surface of the silicon nitride wafers. The required etching rate was 30-80 nm / min. The rest was the same as in Example 1. The specific steps are as follows:

[0032] 1. Substrate preparation: First, the silicon nitride wafer substrate to be etched needs to be cleaned and treated. The purpose of cleaning is to remove impurities and contaminants from the surface to ensure the accuracy and stability of the etching.

[0033] 2. Mask fabrication: A mask layer is coated on the surface of the substrate to protect certain areas from etching. The mask is a photoresist. Photolithography is used to coat the mask material onto the surface of the substrate, and then the desired mask structure is formed through steps such as exposure and development.

[0034] 3. Etching process: The substrate with the mask prepared is immersed in the etching solution. During the etching process, the chemical substances in the etching solution react with the surface of the substrate, that is, Si3N4 reacts with HF, and the generated SiF4 and NH3 gases are continuously extracted.

[0035] After maintaining this position for a period of time, conduct tests to verify whether the etching rate meets the requirements.

[0036] The test results are shown in the table below.

[0037]

[0038] The table above shows that when the amount of hydrogen fluoride used is 60-90g, the etching rate is within the required range.

[0039] Similarly, using succinic anionyl nitrile as a single variable, steps 1-3 of this embodiment were repeated, and the results were shown in the table below.

[0040]

[0041]

[0042] The table above shows that when the amount of succinate is 50-80g, the etching rate is within the required range. Increasing the amount of succinate increases the amount of complexes in the system, reduces hydrofluoric acid hydrolysis, and decreases the etching rate. Conversely, decreasing the amount of succinate increases the amount of free hydrofluoric acid and increases the etching rate.

[0043] Regarding the selection of etching temperatures, the etching solution of Example 1 was used to etch silicon nitride material at different temperatures, and the etching uniformity was calculated using the following formula:

[0044] (Maximum etching depth - Minimum etching depth) / 2 * (Average etching depth) * 100%

[0045] After a 10-minute test, the results are as follows:

[0046]

[0047]

[0048] Test results show that below 40℃, the etching rate is low, but the etching uniformity is good. Above 65℃, the etching uniformity increases rapidly, indicating large etching deviations and a decrease in yield. Considering both speed and quality, the optimal etching temperature is 40-65℃.

[0049] In the actual etching process of silicon nitride chips, controlling the etching temperature can stabilize the etching rate, thus eliminating the need for large quantities of uniformly prepared etching solution. This allows the concentration of effective HF in the solution to remain dynamically stable, thereby reducing the manufacturing difficulty of silicon nitride chips.

[0050] The study also showed that increasing or decreasing the amount of ultrapure water in the solution by 5% would not have a significant impact on the test results.

[0051] This invention is not limited to the above embodiments. Based on the technical solutions disclosed in this invention, those skilled in the art can make some substitutions and modifications to some of the technical features without creative effort, and all such substitutions and modifications are within the protection scope of this invention.

Claims

1. An etching solution for producing a carat-grade silicon nitride chip, characterized by comprising: By weight, it contains 6-9% hydrogen fluoride, 5-8% succinic acid, 15-20% ethanol, and the balance is ultrapure water. ​ 2. The etching solution for the production of carat-grade silicon nitride chips according to claim 1, characterized in that: The etching solution is prepared by first passing hydrogen fluoride gas into ultrapure water at 15-25°C, then adding succinate and ethanol, and stirring for 10-30 minutes. 3.The use method of the etching liquid for car-grade silicon nitride chip production according to claim 1, characterized in that: The etching solution is used for etching the silicon nitride layer and the silicon layer. 4.The use method of the etching liquid for car-grade silicon nitride chip production according to claim 3, characterized in that: Etching is performed at 40-65℃. The etching solution is preheated to 40℃ before etching, and then the temperature is increased according to the rate of hydrogen fluoride consumption during the etching process to keep the H ion concentration in the solution constant. 5.The use method of the etching liquid for car-grade silicon nitride chip production according to claim 3, characterized in that: The etching solution is used to divide the semiconductor chip into individual chips. 6.The use method of the etching liquid for car-grade silicon nitride chip production according to claim 3, characterized in that: The etching solution is used to etch silicon wafers to form silicon nitride chip circuits and components.

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