High selectivity etching solution for silicon dioxide thin films

Abstract

The application discloses a buffer oxidation etching liquid for improving the etching selectivity of THOX oxide film and TEOS oxide film, and the main components are hydrofluoric acid, ammonium fluoride, additive one, additive two and ultrapure water. The etching liquid is used for etching THOX oxide film and TEOS oxide film simultaneously, and can inhibit the etching of the TEOS oxide film. The additive one is adsorbed by reacting with a large number of Si-OH functional groups on the TEOS oxide film, and a protective film hindering the etching of hydrofluoric acid is formed, so that the corrosion of the TEOS oxide film can be effectively inhibited. The additive two can reduce the surface tension of the etching liquid, so that the etching liquid has higher wettability, and the etching uniformity of the etching liquid is increased. The etching liquid has higher selectivity for the THOX oxide film and the TEOS oxide film, and the selectivity of the two can reach 8.32.

Description

Technical Field

[0001] This invention belongs to the field of etching solution technology, and particularly relates to an etching solution for silicon dioxide thin films. Background Technology

[0002] Silicon dioxide, as an environmentally friendly material containing only silicon and oxygen, is easy to synthesize and does not contain any elements harmful to the environment. At the same time, due to its high resistivity, good dielectric strength, excellent chemical and thermal stability, low coefficient of thermal expansion, easily adjustable bandgap, easy integration, and good surface properties, it is widely used in electronic devices, optics, solar cells, thin-film transistors, silicon-on-insulator technology, silicon-on-insulator CMOS, and other fields.

[0003] There are several methods to form silicon dioxide thin films on substrate surfaces. The principles are mainly divided into two types. One is the reaction of the silicon substrate surface with oxygen or a mixture of oxygen and water at high temperatures to form a silicon dioxide thin film (THOX). This film formation method is called thermal oxidation or thermal oxidation. The silicon dioxide thin film produced by this method has a dense structure, good uniformity and repeatability, and strong masking ability, effectively preventing scratches and contamination of devices. The other method is chemical vapor deposition (TEOS) of silicon dioxide films. This method utilizes the self-decomposition of tetraethoxysilane at high temperatures or its reaction with oxygen to deposit a silicon dioxide thin film on the substrate. This film has better step coverage and gap filling characteristics and is often used as a doping barrier or as a dielectric layer between metal layers.

[0004] Etching of silicon dioxide typically uses buffered oxide etchant (BOE), whose main components are hydrofluoric acid, ammonium fluoride, and water, along with small amounts of additives or modifiers. Due to the differences between THOX and TEOS processes, the TEOS film structure is more porous, resulting in a higher etching rate for TEOS films using conventional BOE. However, in certain specialized semiconductor fabrication processes, it is necessary to simultaneously etch both THOX and TEOS layers, requiring a higher etching rate for THOX than for TEOS, a capability that conventional BOE cannot easily achieve. Summary of the Invention

[0005] In response to the problem that conventional BOE etchants have difficulty solving the problem of the etch rate of THOX oxide layer being greater than that of TEOS oxide layer, this invention proposes a BOE etchant combination that improves the selectivity of THOX oxide layer.

[0006] To achieve the above objectives, the present invention provides a BOE etching solution combination scheme, specifically comprising:

[0007] A mixture consisting of 0.5%-5% hydrofluoric acid, 20%-30% ammonium fluoride, ultrapure water, 0.01%-5% thiol compounds, and 0.0001%-0.1% surfactants.

[0008] In the above scheme, the hydrofluoric acid used refers to an electronic-grade hydrofluoric acid solution with a mass fraction of 48%-50%.

[0009] In the above scheme, the ammonium fluoride used refers to an electronic grade ammonium fluoride solution with a mass fraction of 39%-41%.

[0010] In the above scheme, the ultrapure water used refers to ultrapure water with a resistivity of 18 megohms or higher at 25°C.

[0011] In the above scheme, the additive used refers to one or a combination of several monothiols or dithiols, including 4-(pyridin-4-yl)pyrimidine-2-thiol, pyrithiol, panthenol, sec-butanethiol, and 2-pyrimidinethiol.

[0012] In the above scheme, the additive 2 refers to one or a combination of several silanol compounds, including: nonylphenol polyoxyethylene ether methyl silanol, dodecylphenol polyoxyethylene ether methyl silanol, octanol polyoxyethylene ether sulfate methyl silanol, octanol polyoxyethylene ether methoxy silanol, dimethylsiloxane polyethylene glycol methyl silanol, and polyoxypropylene ether methyl silanol.

[0013] The beneficial effects of this invention include:

[0014] (1) The above etching solution is based on conventional BOE etching solution. Hydrofluoric acid is used to etch the silicon oxide layer, and ammonium fluoride is used to maintain the hydrofluoric acid concentration and stabilize the etching rate of the oxide film. The low hydrofluoric acid and high ammonium fluoride system is beneficial to reducing the etching rate of the oxide film and improving the selectivity of THOX oxide film.

[0015] (2) The addition of thiol compounds to the above etching solution can effectively inhibit the etching of TEOS oxide film. Since TEOS oxide film is an amorphous thin film, that is, the lattice structure in its structure is disordered, TEOS oxide film has more surface defects and oxygen vacancies, resulting in more Si-OH adsorption sites in TEOS oxide film; THOX oxide layer has higher density and more ordered lattice structure, with fewer Si-OH adsorption sites. The thiol compounds in the above etching solution can be adsorbed onto the surface of TEOS oxide film in large quantities during the etching process and form a protective film, thereby reducing the etching rate of TEOS oxide film and increasing the selectivity of THOX oxide film.

[0016] (3) The surfactant in the above etching solution can effectively reduce the surface tension of the etching solution, increase the wettability of the etching solution, improve the etching uniformity, and enhance the etching effect of the etching solution in microstructures. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure to be etched.

[0018] Figure 2 This is a schematic diagram of the structure after etching with the etching solution in Example 1.

[0019] Figure 3 This is a schematic diagram of the structure after etching with the etching solution in Comparative Example 3. Detailed Implementation

[0020] The technical solution of the present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments. It is worth noting that the following embodiments are only some preferred embodiments of the present invention and should not be construed as limiting the present invention. The scope of protection of the present invention should be determined by the contents of the claims. Modifications and substitutions made by those skilled in the art to the technical solution of the present invention without creative effort all fall within the scope of protection of the present invention.

[0021] First, prepare the etching solution according to its composition and stir for 60 minutes. Place the PFA bottle containing the etching solution in a low-temperature constant temperature bath (25℃) and keep it at that temperature for 3 hours. Then, immerse the two types of silicon oxide thin film wafers in the etching solution and slowly stir to etch them. The thickness of the silicon oxide thin film wafers before and after etching is measured using an ellipsometry. The corresponding etching rate is calculated based on the thickness difference before and after etching / etching time.

[0022] Surface tension testing: The surface tension of the etching solution at 25°C was measured using a surface tension meter.

[0023] To better understand the present invention, the following will further illustrate the content of the present invention with reference to the embodiments. However, the content of the present invention is not limited to the following embodiments and comparative examples. Some embodiments and comparative examples conceived in the present invention are shown in Table 1 below.

[0024] Table 1

[0025] Serial Number hydrofluoric acid wt% ammonium fluoride wt% Additives (wt%) Additive 2 wt% Water wt% Example 1 1 22 4-(pyridin-4-yl)pyrimidine-3-thiol 0.01 Dimethylsiloxane, polyethylene glycol, methylsilanol 0.005 margin Example 2 1 22 4-(pyridin-4-yl)pyrimidine-3-thiol 0.1 Dimethylsiloxane, polyethylene glycol, methylsilanol 0.05 margin Example 3 1 22 4-(pyridin-4-yl)pyrimidine-3-thiol 1 Dimethylsiloxane, polyethylene glycol, methylsilanol 0.07 margin Example 4 1 22 4-(pyridin-4-yl)pyrimidine-3-thiol 5 Dimethylsiloxane, polyethylene glycol, methylsilanol 0.1 margin Example 5 1 22 Pyrithione 0.05 Dimethylsiloxane, polyethylene glycol, methylsilanol 0.005 margin Example 6 2 22 Pyrithione 0.05 Dimethylsiloxane, polyethylene glycol, methylsilanol 0.07 margin Example 7 1 22 0.2% pyrithione Dimethylsiloxane, polyethylene glycol, methylsilanol 0.1 margin Example 8 1 22 Panthenyl thiol 0.04 Octyl alcohol polyoxyethylene ether methoxysilane alcohol 0.07 margin Example 9 1 22 sec-Butyl mercaptan 0.05 Dodecylphenol polyoxyethylene ether methylsilanol 0.05 margin Example 10 1 23 2-Pyrimidinethiol 0.01 Dodecylphenol polyoxyethylene ether methylsilanol 0.05 margin Example 11 2 24 2-Pyrimidinethiol 0.05 Dodecylphenol polyoxyethylene ether methylsilanol 0.1 margin Example 12 1 22 2-Pyrimidinethiol 0.1 Dodecylphenol polyoxyethylene ether methylsilanol 1 margin Comparative Example 1 1 22 - - margin Comparative Example 2 1 22 4-(pyridin-4-yl)pyrimidine-3-thiol 1 - margin Comparative Example 3 1 22 - Dimethylsiloxane, polyethylene glycol, methylsilanol 0.07 margin Comparative Example 4 0.5 18 3-(triethoxysilyl)-1-propanethiol 0.1 Dimethylsiloxane, polyethylene glycol, methylsilanol 0.05 margin Comparative Example 5 1 25 Hexanedithiol 2 Octyl alcohol polyoxyethylene ether methoxysilane alcohol 0.07 margin Comparative Example 6 5 18 1.5g of n-undecyl mercaptan Dodecylphenol polyoxyethylene ether methylsilanol 0.05 margin Comparative Example 7 3 20 2-Ethylhexylthiol 1 Polyoxypropylene ether methylsilanol 0.01 margin

[0026] The properties of the etching solutions prepared for each embodiment and comparative example, the etching rate of each film layer, the selectivity, and the surface tension results are shown in Table 2.

[0027] Table 2.

[0028] Serial Number Etching solution properties TEOS membrane rate Å / min THOX membrane rate Å / min Selection ratio tension mN / m Example 1 clarify 24.238 177.663 7.33 39.12 Example 2 clarify 19.753 157.432 7.97 37.54 Example 3 clarify 16.896 145.954 8.32 35.88 Example 4 turbid 19.306 140.576 7.56 30.58 Example 5 clarify 17.650 143.847 8.15 43.63 Example 6 clarify 19.883 157.471 7.92 39.47 Example 7 turbid 15.718 139.732 8.89 35.68 Example 8 clarify 27.075 142.414 5.26 36.67 Example 9 clarify 26.221 146.312 5.58 34.06 Example 10 clarify 17.706 153.691 8.68 35.67 Example 11 clarify 26.995 165.477 6.13 33.82 Example 12 turbid 16.481 147.668 8.96 32.48 Comparative Example 1 clarify 420.384 210.341 0.50 77.23 Comparative Example 2 turbid 73.903 197.322 2.67 62.11 Comparative Example 3 clarify 252.301 204.364 0.81 40.91 Comparative Example 4 clarify 18.829 100.361 5.33 37.32 Comparative Example 5 clarify 23.163 151.484 6.54 32.54 Comparative Example 6 turbid 59.031 427.382 7.24 33.21 Comparative Example 7 turbid 47.290 345.687 7.31 41.23

[0029] Comparing the above examples and comparative examples, it can be seen that Examples 1 to 4 show that 4-(pyridin-4-yl)pyrimidine-2-thiol has a significant inhibitory effect on the etching rate of TEOS film. The selectivity ratio of the two films is between 7.33 and 8.32. When its content is 1%, the selectivity ratio reaches the highest of 8.32. However, further increasing the amount added will cause the etching solution to become turbid, making the etching solution unusable. At the same time, the relatively low concentration of hydrofluoric acid reduces the etching rate of the two oxide films and enhances the inhibitory effect of 4-(pyridin-4-yl)pyrimidine-2-thiol on the etching rate of TEOS film. The combination of dimethylsiloxane polyethylene glycol methylsilanol and 4-(pyridin-4-yl)pyrimidine-2-thiol can reduce the tension of the etching solution while increasing the selectivity ratio. In Examples 1 to 4, the tension is between 30.58 and 39.12.

[0030] Examples 5 to 7 show that the combination of pyrithione and dimethylsiloxane polyethylene glycol methylsilanol also has a better inhibitory effect on the etching of TEOS film. When the addition amount of the two is 0.05wt% and 0.005wt% respectively, the selectivity ratio of TOX to TEOS can reach 8.15, and the tension is slightly high at 43.63mN / m. Increasing the addition amount of pyrithione can increase the selectivity ratio, but it will also lead to turbidity of the etching solution. Increasing the amount of dimethylsiloxane polyethylene glycol methylsilanol can improve the tension, but it will also slightly reduce the etching selectivity ratio of the two.

[0031] Examples 10 to 12 show that the combination of 2-pyrimidine mercaptan and dodecylphenol polyoxyethylene ether methylsilanol has a similar effect. When the amount of 2-pyrimidine mercaptan added is 0.01 wt%, the selectivity ratio can reach 8.68. Simultaneously, adjusting the concentrations of 2-pyrimidine mercaptan and hydrofluoric acid can control the etching rate and selectivity ratio of the oxide film. However, with the increase of the amount of 2-pyrimidine mercaptan added, the etching solution becomes turbid, affecting its use. The addition of dodecylphenol polyoxyethylene ether methylsilanol also reduces the surface tension of the etching solution to 32.48. The above examples are a partial list of experimental data from the combination of additive one and additive two; their selectivity ratios are all above 5, and the surface tension is within a suitable range.

[0032] Comparative Example 1, lacking additives, showed no inhibitory effect on the etching rate of the TEOS film and exhibited high surface tension. In Comparative Example 2, additive two was not included in the formulation, resulting in high surface tension of the etching solution, but the solution still showed some inhibitory effect on the TEOS film. In Comparative Example 3, additive one was not included in the formulation, and the selectivity ratio of 0.81 indicates that using dimethylsiloxane-polyethylene glycol methylsilanol alone also has a certain inhibitory effect. Comparative Examples 4 to 7 demonstrate that the structures of additive one and additive two significantly influence the inhibitory effect on TEOS film etching. Additive one with more branched chains and longer carbon chains exhibits better inhibitory effects, while additive two with more oxygen atoms results in lower surface tension and better etching uniformity.

[0033] Obviously, the above embodiments and comparative examples are merely illustrative examples and are not intended to limit the scope of the invention. Those skilled in the art will recognize numerous variations and combinations of the above embodiments, and it is neither necessary nor possible to list all possible embodiments here. Therefore, any changes or modifications made based on the above embodiments are still within the scope of protection of this invention.

Claims

1. A buffered oxide etching solution for silicon dioxide etching, characterized in that, The buffered oxidation etching solution includes 0.5%-5% hydrofluoric acid, 20%-30% ammonium fluoride, 0.01%-5% thiol compounds, 0.0001%-0.1% surfactant, and the balance being ultrapure water. The thiol compound is selected from one or a combination of several of 4-(pyridin-4-yl)pyrimidin-2-thiol, pyrithiol, panthenol, sec-butyritol, and 2-pyrimidinthiol; The surfactant is selected from one or a combination of several of the following: nonylphenol polyoxyethylene ether methyl silanol, dodecylphenol polyoxyethylene ether methyl silanol, octanol polyoxyethylene ether sulfate methyl silanol, octanol polyoxyethylene ether methoxy silanol, dimethylsiloxane polyethylene glycol methyl silanol, and polyoxypropylene ether methyl silanol.

2. The etching solution according to claim 1, characterized in that: The hydrofluoric acid used in the etching solution refers to an electronic-grade hydrofluoric acid solution with a mass fraction of 48%-50%.

3. The etching solution according to claim 1, characterized in that: The ammonium fluoride used in the etching solution refers to an electronic-grade ammonium fluoride solution with a mass fraction of 39%-41%.

4. The etching solution according to claim 1, characterized in that: The ultrapure water used in the etching solution refers to ultrapure water with a resistivity of 18 megohms or higher at 25°C.

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