BOE etching solution with high silicon oxide / silicon nitride selection ratio

Abstract

The invention discloses a BOE etching solution with a high silicon oxide / silicon nitride selection ratio, and the BOE etching solution comprises the following components in percentage by mass: 2%-20% of hydrofluoric acid, 17%-20% of ammonium fluoride, 0.01%-0.5% of an additive, 0.003%-0.3% of a defoaming agent and the balance of ultrapure water. The additive is aromatic aldehyde, so that the selection ratio of silicon oxide to silicon nitride can be effectively improved; the defoaming agent is used for improving foam and uniformly dispersing aromatic aldehyde in the BOE etching solution, so that the uniformity of the solution is ensured. The BOE etching solution in the invention can ensure that the silicon nitride layer is less etched, and plays a role in improving the selection ratio of silicon oxide / silicon nitride.

Description

Technical Field

[0001] The invention belongs to the field of electronic chemicals, and in particular relates to a BOE etching solution with a high silicon oxide / silicon nitride selectivity ratio. Background Art

[0002] In the chip manufacturing process, the precise construction of multi-layer structures is the key to ensuring chip performance. It is a common process to alternately deposit silicon oxide layers and silicon nitride layers on a substrate and then use etching technology to form a specific structure. However, since BOE (Buffered Oxide Etchant) usually contains hydrofluoric acid, ammonium fluoride, water and additives, it has a high efficiency in etching the silicon oxide layer, but it also produces a certain degree of etching on the silicon nitride layer, which may lead to structural inaccuracies and unstable performance. Summary of the invention In order to solve the above problems, the present invention aims to provide a BOE etching solution with a high silicon oxide / silicon nitride selectivity ratio.

[0003] The technical solution of the present invention is as follows: The invention relates to a BOE etching solution with a high silicon oxide / silicon nitride selectivity ratio. The BOE etching solution comprises 2-20% hydrofluoric acid, 17-20% ammonium fluoride, 0.01-0.5% additives and 0.003-0.3% defoaming agent, accounting for 2-20% of the total weight of the etching solution.

[0004] Furthermore, the present invention relates to the above etching solution, wherein the concentration of hydrofluoric acid is 49%, the concentration of ammonium fluoride is 40%, and the rest is ultrapure water.

[0005] Furthermore, the present invention relates to the above etching solution, wherein the additive content is preferably 0.03-0.1%.

[0006] Furthermore, the present invention relates to the above etching solution, wherein the additive comprises at least one of benzaldehyde, p-methylbenzaldehyde, 2,4-dimethylbenzaldehyde and the like.

[0007] Furthermore, the present invention relates to the above etching solution, wherein the defoaming agent content is preferably 0.03-0.3%. The defoaming agent is polyethylene glycol.

[0008] When the etching solution of the present invention is used to etch the silicon oxide layer, the etching temperature is 20-25° C. and the etching time is 10-30 minutes.

[0009] When the etching solution of the present invention is used to etch the silicon nitride layer, the etching temperature is 20-25° C. and the etching time is 10-30 minutes.

[0010] The etching solution of the present invention is used to improve the silicon oxide / silicon nitride selection ratio. In order to verify the effect of the etching solution, the present invention uses wafer samples deposited with silicon oxide and silicon nitride films to carry out etching experiments.

[0011] The advantages of the present invention are: a "protective agent" is added to the BOE etching solution, and the protective agent can effectively reduce or inhibit the etching of the silicon nitride layer, while not affecting the etching efficiency of the silicon oxide layer, so as to improve the silicon oxide / silicon nitride selectivity. The selection of this protective agent is very important, and it needs to have a high degree of selectivity and stability, and can form a protective film during the etching process, covering the surface of the silicon nitride layer, and inhibiting the etching of the BOE etching solution. By optimizing the formula of the BOE etching solution and adding the protective agent, selective etching of the silicon oxide layer and the silicon nitride layer can be achieved, thereby accurately controlling the structure and performance of the chip. This is of great significance for improving the reliability of the chip and reducing the manufacturing cost.

[0012] According to the reaction mechanism of hydrofluoric acid and silicon nitride, etching is carried out by continuously breaking Si-N bonds. This breaking occurs by inserting an HF molecule into the initial Si-N bond, thereby forming a Si-F bond and an NH bond. When aromatic aldehydes are added, they react with the amino groups on the surface of silicon nitride. The reaction mechanism is as follows: Figure 2 As shown, the benzene ring of aromatic aldehydes can form steric hindrance, effectively preventing the formation of Si-F bonds, thereby protecting silicon nitride from being etched. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 The reaction mechanism of hydrofluoric acid etching of silicon nitride film.

[0013] Figure 2 Schematic diagram of the principle of aromatic aldehydes protecting silicon nitride from etching. DETAILED DESCRIPTION

[0014] 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 creative work belong to the protection scope of the present invention.

[0015] For ease of operation, the total amount of BOE etching solution prepared is 100g, and a large amount of preparation is made according to this method in production. The etching temperature is 20℃, and the etching time of the sample is 20min. The etching rate of silicon oxide and silicon nitride samples is calculated according to formula ①.

[0016] Etching rate = (film thickness before etching - film thickness after etching) / etching time formula ① The raw materials were added in the order of ultrapure water, ammonium fluoride, and hydrofluoric acid. After stirring and mixing evenly, aromatic aldehyde and polyethylene glycol were added respectively. After stirring and mixing for 5 minutes, the etching experiment was carried out.

[0017] Before and after etching, the samples were cleaned with ultrapure water and dried with nitrogen. The thickness of the samples before and after etching was tested using an ellipsometer, and the etching rate of the samples was calculated using formula ①.

[0018] The technical solution of the present invention is further described below in conjunction with the examples. The contents of the components and the etching rates of the examples and comparative examples are shown in Table 1, where the components are calculated by mass percentage, and the balance is ultrapure water.

[0019] Table 1

[0020] The results of the embodiments and comparative examples show that the addition of additives and defoamers can improve the selectivity of silicon oxide / silicon nitride to a certain extent. Moreover, within a certain range of hydrofluoric acid and ammonium fluoride concentrations, there is a relatively obvious improvement effect. When there is only polyethylene glycol in the system and no aromatic alcohol is present, there is almost no effect on the selectivity of silicon oxide and silicon nitride. If only aromatic aldehydes are added, the solution homogeneity is poor, the surface of the wafer is uneven after etching, and the etching rate cannot be calculated. In addition, the addition of hydroxymethyl cellulose can extend the carbon chain, produce steric hindrance, and inhibit the etching of silicon nitride, thereby improving the selectivity to a certain extent.

[0021] 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 BOE etching solution with a high silicon oxide / silicon nitride selectivity ratio, characterized in that: The BOE etching solution comprises the following components according to mass percentage: 2-20% hydrofluoric acid, 17-20% ammonium fluoride, 0.01-0.5% additives, 0.003-0.3% defoaming agent, and the rest is ultrapure water.

2. The BOE etching solution with a high silicon oxide / silicon nitride selectivity ratio according to claim 1, characterized in that: The concentration of the hydrofluoric acid is 45-55%, and the concentration of the ammonium fluoride is 35-45%.

3. The BOE etching solution with a high silicon oxide / silicon nitride selectivity ratio according to claim 2, characterized in that: The etching solution has a hydrofluoric acid concentration of 49% and an ammonium fluoride concentration of 40%.

4. The BOE etching solution with a high silicon oxide / silicon nitride selectivity ratio according to claim 1, characterized in that: The additive includes at least one of benzaldehyde, p-methylbenzaldehyde, 2,4-dimethylbenzaldehyde and the like.

5. The BOE etching solution with a high silicon oxide / silicon nitride selectivity ratio according to claim 4, characterized in that: The content of the additive is preferably 0.03-0.1%.

6. The BOE etching solution with a high silicon oxide / silicon nitride selectivity ratio according to claim 1, characterized in that: The defoaming agent is polyethylene glycol.

7. The BOE etching solution with a high silicon oxide / silicon nitride selectivity ratio according to claim 6, characterized in that: The defoamer content is preferably 0.03-0.3%.

8. The BOE etching solution with a high silicon oxide / silicon nitride selectivity ratio according to claim 1, characterized in that: The resistance of the ultrapure water is not less than 18 MΩ·cm, and the salt content in the ultrapure water is not higher than 0.3 mg / L.

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