Bos etching solution with high silicon oxide / silicon nitride selectivity

Abstract

The application discloses a BOE etching solution with high silicon oxide / silicon nitride selectivity, which 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 rest of ultrapure water. The additive is aromatic aldehyde, which can effectively improve the selectivity of silicon oxide to silicon nitride; the defoaming agent can improve the foam and uniformly disperse the aromatic aldehyde in the BOE etching solution, thereby ensuring the uniformity of the solution. The BOE etching solution can ensure that the silicon nitride layer is less etched, thereby improving the selectivity of silicon oxide to silicon nitride.

Description

Technical Field

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

[0002] In chip manufacturing processes, the precise construction of multilayer structures is crucial for ensuring chip performance. A common process flow involves alternating deposition of silicon oxide and silicon nitride layers on a substrate, followed by etching to form specific structures. However, BOE (Buffered Oxide Etchant), which typically contains hydrofluoric acid, ammonium fluoride, water, and additives, while highly efficient at etching silicon oxide layers, also etches silicon nitride layers to some extent. This can lead to structural inaccuracies and performance instability. Summary of the Invention To address the aforementioned 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 this invention is as follows: This 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% defoamer by weight of the total etching solution.

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

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

[0006] Furthermore, the present invention relates to the above-mentioned etching solution, wherein the additives include at least one of benzaldehyde, p-methylbenzaldehyde, 2,4-dimethylbenzaldehyde, etc.

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

[0008] When etching the silicon oxide layer using the etching solution of the present invention, the etching temperature is 20-25℃ and the etching time is 10-30min.

[0009] When etching the silicon nitride layer using the etching solution of the present invention, the etching temperature is 20-25℃ and the etching time is 10-30min.

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

[0011] The advantage of this invention lies in the addition of a "protective agent" to the BOE etching solution. This agent effectively reduces or inhibits the etching of the silicon nitride layer without affecting the etching efficiency of the silicon oxide layer, thereby improving the silicon oxide / silicon nitride selectivity ratio. The selection of this protective agent is crucial; it needs to possess high selectivity and stability, forming a protective film during the etching process to cover the silicon nitride layer surface and inhibit the etching by the BOE etching solution. By optimizing the BOE etching solution formulation and adding the protective agent, selective etching of both the silicon oxide and silicon nitride layers can be achieved, thereby precisely controlling the chip's structure and performance. This is of great significance for improving chip reliability and reducing manufacturing costs.

[0012] Based on the reaction mechanism of hydrofluoric acid and silicon nitride, etching occurs through the continuous breaking of Si-N bonds. This breaking happens by inserting an HF molecule into the initial Si-N bond, thereby forming Si-F and NH bonds. Upon the addition of aromatic aldehydes, they react with amino groups on the silicon nitride surface, and the reaction mechanism is as follows... Figure 2 As shown, the benzene ring in aromatic aldehydes can form steric hindrance, effectively preventing the formation of Si-F bonds and thus protecting silicon nitride from etching. Attached Figure Description Figure 1 The reaction mechanism for etching silicon nitride films with hydrofluoric acid.

[0013] Figure 2 A schematic diagram illustrating the principle of how aromatic aldehydes protect silicon nitride from etching. Detailed Implementation

[0014] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. These embodiments are merely some, not all, of the present invention. 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.

[0015] For ease of operation, the total amount of BOE etching solution prepared was 100g. Large-scale production was carried out using this method. The etching temperature was 20℃, and the etching time for the samples was 20min. The etching rates of the silicon oxide and silicon nitride samples were calculated using formula ①.

[0016] Etching rate = (film thickness before etching - film thickness after etching) / etching time (Formula ①) The raw materials were added in the following order: ultrapure water, ammonium fluoride, and hydrofluoric acid. After stirring and mixing evenly, aromatic aldehydes and polyethylene glycol were added separately. 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 measured using an elliptic polarization spectrometer. The etching rate of the samples was calculated using formula ①.

[0018] The technical solution of the present invention will be further described below with reference to the embodiments. The content of each component and the etching rate of the embodiments and comparative examples are shown in Table 1. The components are expressed as mass percentages, and the balance is ultrapure water.

[0019] Table 1

[0020] The results of the examples and comparative examples show that the addition of additives and defoamers can improve the selectivity ratio of silicon oxide / silicon nitride to some extent. Furthermore, within a certain range of hydrofluoric acid and ammonium fluoride concentrations, there is a significant improvement effect. When only polyethylene glycol is present in the system, without aromatic alcohols, there is almost no effect on the selectivity ratio of silicon oxide and silicon nitride. If only aromatic aldehydes are added, the solution homogeneity is poor, resulting in uneven wafer surfaces after etching, making it impossible to calculate the etching rate. In addition, the addition of hydroxymethyl cellulose can extend the carbon chain, creating steric hindrance and inhibiting the etching of silicon nitride, thereby improving the selectivity ratio to some extent.

[0021] The technical solutions of the present invention have been 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 those skilled in the art based on the present invention, or equivalent substitutions for the materials selected in the present invention, fall within the scope of patent protection.

Claims

1. A BOE etching solution with a high silicon oxide / silicon nitride selectivity ratio, characterized in that: The BOE etching solution comprises, by weight percentage, 2-20% hydrofluoric acid, 17-20% ammonium fluoride, 0.01-0.5% additives, 0.003-0.3% defoamer, and the remainder is ultrapure water. The additives include at least one of benzaldehyde, p-methylbenzaldehyde, and 2,4-dimethylbenzaldehyde; the defoamer is polyethylene glycol.

2. The BOE etching solution with a high silicon oxide / silicon nitride selectivity ratio according to claim 1, characterized in that, The concentration of hydrofluoric acid is 45-55%, and the concentration of 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 content is 0.03-0.1%.

5. The BOE etching solution with a high silicon oxide / silicon nitride selectivity ratio according to claim 1, characterized in that, The defoamer content is 0.03-0.3%.

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

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