Etching liquid for selectively etching silicon nitride and titanium nitride and preparation method thereof

Abstract

The application relates to the technical field of semiconductor and electronic chemicals, and particularly discloses an etching solution for selectively etching silicon nitride and titanium nitride and a preparation method thereof. The etching solution contains the following components in percentage by mass: 10-45% of phosphoric acid, 1-5% of hydrofluoric acid, 0.5-2.5% of a pH buffer, 0.01-1.8% of a solubilizer and 0.1-7% of an etching inhibitor, and the rest is water. The pH buffer can effectively stabilize the pH of the etching solution, the solubilizer can improve the solubility of the solvent in the etching solution, reduce the tension of the solid-liquid phase interface in the solution and promote the transmission rate of the interphase substances, and the etching inhibitor can form a film on the surface of the titanium nitride in the form of a coordination bond, so that the silicon nitride and the titanium nitride have a high selectivity ratio. The etching solution can inhibit the etching rate of the titanium nitride under the condition of a high etching rate of the silicon nitride, and can ensure the high selectivity ratio of the silicon nitride and the titanium nitride.

Description

Technical Field

[0001] This invention belongs to the field of electronic chemicals technology, specifically relating to an etching solution for selectively etching silicon nitride and titanium nitride and its preparation method. Background Technology

[0002] Silicon nitride (SiN) possesses excellent thermal, mechanical, and chemical stability, making it widely used in high-temperature, high-power, and high-frequency electronic devices. Its wide bandgap allows for tuning of its conductivity through doping, thus making it a crucial semiconductor material. Titanium nitride exhibits good metal diffusion blocking properties and low resistivity after annealing, finding various applications in the semiconductor industry, such as hard masks, metal barrier layers, conductive electrodes, and metal gates. Furthermore, titanium nitride is used in advanced process chips to enhance transistor performance.

[0003] The semiconductor industry has developed rapidly in recent years. With the continuous miniaturization of semiconductor devices and feature sizes, there is a need to improve and refine current semiconductor manufacturing methods and processes. Etching technology, as the most stable, effective, and widely used technique for semiconductor materials, has been employed by the industry for a long time. During etching, it is crucial to strictly control the etching process time while ensuring that the barrier layer is not etched away as much as possible. The ratio of the etching rate of silicon nitride to the etching rate of the barrier layer titanium nitride is called the etch selectivity ratio. A higher ratio is more beneficial to improving product yield. However, as the semiconductor industry's requirements for product yield become increasingly stringent, how to increase the etching rate of silicon nitride while minimizing the etching of the barrier layer titanium nitride has become a pressing problem to be solved in this field.

[0004] CN 113604803 A discloses an etching solution for selectively etching tungsten and titanium nitride, comprising hydrogen peroxide, hydrogen peroxide stabilizer, nitric acid, organic acid, etching inhibitor, surfactant, and deionized water. Using this etching solution at 50°C, tungsten and titanium nitride were etched. The results showed that the etching solution could etch metallic tungsten at a high rate while suppressing the etching rate of titanium nitride, thus maintaining a high selectivity. CN117720925A discloses a trench buffer etching solution for inhibiting titanium nitride corrosion. Its main components are hydrofluoric acid, ammonium fluoride, organic amine, surfactant, and ultrapure water. Using this etching solution at 25°C, silicon oxide and titanium nitride were etched. The results showed that the etching solution has high selectivity for both silicon oxide and titanium nitride layers. While etching silicon oxide trenches cleanly without residue, it can slow down the corrosion of the titanium nitride layer, achieving etching of trench structures requiring high selectivity. While current etching inhibitors can slow down the etching rate of titanium nitride in acidic etchant systems to some extent, the semiconductor industry has placed higher demands on the etching rate of titanium nitride in acidic etchant systems as semiconductor processes gradually advance from 28nm to 14nm and 7nm. Furthermore, due to the chemically stable nature of silicon nitride described in this invention, rapid etching can only be achieved in high-temperature acidic solutions above 100°C. Therefore, developing a high-selectivity etchant with excellent overall performance is particularly urgent. Summary of the Invention

[0005] This invention provides an etching solution for selectively etching silicon nitride and titanium nitride, and a method for preparing the same. The etching solution can efficiently etch silicon nitride at high temperatures above 100°C, while simultaneously suppressing the chemical and electrochemical corrosion of titanium nitride by the etching solution. This significantly slows down the etching rate of titanium nitride in the high-temperature etching solution, and can partially or completely remove the silicon nitride structure without significantly damaging the titanium nitride structure, thereby achieving a high etching selectivity ratio for silicon nitride and titanium nitride.

[0006] The technical solution of the present invention is to provide an etching solution for selectively etching silicon nitride and titanium nitride, the etching solution containing the following components by mass percentage: 10-45% phosphoric acid, 1-5% hydrofluoric acid, 0.5-2.5% pH buffer, 0.01-1.8% solubilizer and 0.1-7% etching inhibitor, with the balance being water.

[0007] In some of these embodiments, the phosphoric acid is electronic-grade phosphoric acid with a mass concentration of 70-95%.

[0008] In some embodiments, the hydrofluoric acid is electronic-grade hydrofluoric acid with a mass concentration of 20-50%. In some of these embodiments, the pH buffer is one or a combination of several of ammonium tartrate, sodium oxalate, sodium phosphate, sodium acetate, and hexamethylenetetramine.

[0009] In some of these embodiments, the solubilizer is one or a combination of several of polyethylene glycol 400, polyethylene glycol 600, sodium dodecyl sulfate, polyacrylamide, octadecyl vinyl ether, diethyl phosphate, triethanolamine, nonylphenol polyoxyethylene ether, and lauryl alcohol polyoxyethylene ether.

[0010] In some of these embodiments, the etching inhibitor is one or a combination of several of thiazole, 2-amino-1,3,4-thiadiazole, 2,2-bipyridine, 2-mercaptoimidazole, 4-pyridine, imidazoline, 2-aminopyridine, 2-imidazolidinone, and benzotriazole.

[0011] In some of these embodiments, the water is ultrapure water.

[0012] In a preferred embodiment, the etching solution contains sodium phosphate as the pH buffer, lauryl alcohol polyoxyethylene ether as the solubilizer, and 2-imidazolidineone as the etching inhibitor.

[0013] The present invention also relates to a method for preparing the etching solution, wherein phosphoric acid, hydrofluoric acid and water are mixed in proportion, and then an etching inhibitor, a solubilizer and a pH buffer are added in sequence and mixed. After sealing, the solution is stored for 4 to 8 hours to obtain the solution.

[0014] The present invention has the following beneficial effects: 1. Compared with existing etching processes, the present invention provides an etching solution for selectively etching silicon nitride and titanium nitride. While ensuring that the etching solution rapidly etches silicon nitride at high temperatures above 100°C, it suppresses the chemical and electrochemical corrosion of titanium nitride by the etching solution, greatly slowing down the etching rate of titanium nitride in the high-temperature etching solution, and achieving etching stability and uniformity.

[0015] 2. The solubilizer in the etching solution of this invention can effectively improve the solubility of the solvent in the etching solution, reduce the tension of the solid-liquid interface in the solution, promote the transfer rate of interphase materials, and ensure the etching effect of silicon nitride.

[0016] 3. The etching inhibitor in the etching solution of the present invention can form an etching protective layer on the surface of titanium nitride in the form of coordination bonds with the metal, which greatly reduces the etching rate of titanium nitride by the etching solution and ensures that silicon nitride and titanium nitride have a high etching selectivity. Detailed Implementation

[0017] The present invention will now be described in detail with reference to specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0018] Example 1 An etching solution for selectively etching silicon nitride and titanium nitride, comprising the following: 40wt% phosphoric acid, 4.5wt% hydrofluoric acid, 1.5wt% sodium oxalate, 0.1wt% polyacrylamide, 0.1wt% thiazole, and the remainder is ultrapure water.

[0019] Example 2 An etching solution for selectively etching silicon nitride and titanium nitride, comprising the following: 30wt% phosphoric acid, 4.5wt% hydrofluoric acid, 1.5wt% sodium oxalate, 0.1wt% polyacrylamide, 0.1wt% thiazole, and the remainder is ultrapure water.

[0020] Example 3 An etching solution for selectively etching silicon nitride and titanium nitride, comprising the following: 40wt% phosphoric acid, 2.5wt% hydrofluoric acid, 1.0wt% sodium oxalate, 0.1wt% polyacrylamide, 0.1wt% thiazole, and the remainder is ultrapure water.

[0021] Example 4 An etching solution for selectively etching silicon nitride and titanium nitride, comprising the following: 40wt% phosphoric acid, 3.5wt% hydrofluoric acid, 1.0wt% sodium phosphate, 0.05wt% sodium dodecyl sulfate, 0.2wt% 2-amino-1,3,4-thiadiazole, and the remainder is ultrapure water.

[0022] Example 5 An etching solution for selectively etching silicon nitride and titanium nitride, comprising the following: 40wt% phosphoric acid, 3.5wt% hydrofluoric acid, 1.0wt% sodium phosphate, 0.05wt% octadecyl vinyl ether, 0.2wt% 4-pyridine, and the remainder is ultrapure water.

[0023] Example 6 An etching solution for selectively etching silicon nitride and titanium nitride, comprising the following: 40wt% phosphoric acid, 3.5wt% hydrofluoric acid, 1.0wt% sodium phosphate, 0.05wt% polyethylene glycol 600, 0.2wt% imidazoline, and the remainder is ultrapure water.

[0024] Example 7 An etching solution for selectively etching silicon nitride and titanium nitride, comprising the following: 40wt% phosphoric acid, 3.5wt% hydrofluoric acid, 1.0wt% sodium phosphate, 0.05wt% lauryl alcohol polyoxyethylene ether, 0.2wt% 2-imidazolidineone, and the remainder is ultrapure water.

[0025] Example 8 An etching solution for selectively etching silicon nitride and titanium nitride, comprising the following: 40wt% phosphoric acid, 3.5wt% hydrofluoric acid, 1.0wt% sodium acetate, 0.05wt% polyacrylamide, 0.2wt% benzotriazole, and the remainder is ultrapure water.

[0026] Example 9 9-1. Based on Example 7, the only difference is that lauryl alcohol polyoxyethylene ether is replaced with an equal amount of polyacrylamide; 9-2. Based on Example 7, the only difference is that the amount of lauryl alcohol polyoxyethylene ether is adjusted to 1 wt%; 9-3. Based on Example 7, the only difference is that 2-imidazolidineone is replaced with an equal amount of thiazole; 9-4. Based on Example 7, the only difference is that 2-imidazolidineone is replaced with an equal amount of imidazoline; 9-5. Based on Example 7, the only difference is that the amount of 2-imidazolidineone is adjusted to 5 wt%; 9-6. Based on Example 7, the only difference is that sodium phosphate is replaced with an equal amount of hexamethylenetetramine; 9-7. Based on Example 7, the only difference is that the amount of sodium phosphate is adjusted to 2.5 wt%; Comparative Example 1 An etching solution comprising the following components: 45 wt% phosphoric acid, 4 wt% hydrofluoric acid, and the remainder being ultrapure water.

[0027] Comparative Example 2 An etching solution comprising: 45 wt% phosphoric acid, 4 wt% hydrofluoric acid, 0.1 wt% sodium oxalate, and the remainder being ultrapure water.

[0028] Comparative Example 3 An etching solution comprising: 45 wt% phosphoric acid, 4 wt% hydrofluoric acid, 0.1 wt% sodium oxalate, 2.5 wt% polyacrylamide, with the remainder being ultrapure water.

[0029] Comparative Example 4 An etching solution comprising: 40 wt% phosphoric acid and 3.5 wt% hydrofluoric acid, with the remainder being ultrapure water.

[0030] Comparative Example 5 An etching solution comprising the following components: 40 wt% phosphoric acid, 3.5 wt% hydrofluoric acid and 1.0 wt% sodium phosphate, with the remainder being ultrapure water.

[0031] Comparative Example 6 An etching solution comprising the following components: 40 wt% phosphoric acid, 3.5 wt% hydrofluoric acid, 1.0 wt% sodium phosphate, 0.05 wt% lauryl alcohol polyoxyethylene ether, with the remainder being ultrapure water.

[0032] When preparing the above etching solution, first mix phosphoric acid, hydrofluoric acid and ultrapure water in proportion. Then, slowly add the etching inhibitor and solubilizer in sequence while continuously stirring. Finally, add the pH buffer and stir evenly. After sealing, store at 25°C for 6 hours.

[0033] The etching solutions used in the above embodiments and comparative examples were used to etch silicon nitride and titanium nitride samples. Specifically, after cleaning and drying, the initial thicknesses of the cut silicon nitride and titanium nitride samples were measured using an ellipsometry and a four-probe thickness gauge, respectively. The samples were then fixed in etching supports and etched in an etching solution at 100°C for 10 minutes. After removal, they were rinsed with ultrapure water at 70°C for 10 seconds and then dried with nitrogen. The thicknesses of silicon nitride and titanium nitride after etching were measured, and the corresponding etching rate was calculated by comparing the changes in sample thickness before and after etching. Specific details are shown in Table 1 below.

[0034] Table 1

[0035] The data in the table show that in Comparative Example 1, without the addition of pH buffer, solubilizer, and etching inhibitor, the etching rates of silicon nitride and titanium nitride were unstable. The etching rate of titanium nitride gradually increased with time, resulting in a high etching rate and a low etching selectivity. In Comparative Example 2, sodium oxalate was added as a pH buffer, which effectively alleviated the problem of unstable etching rates, and the etching rate of titanium nitride was significantly reduced. In Comparative Example 3, polyacrylamide was added as a solubilizer to adjust the surface tension between the etching solution and the solid phase, which increased the wettability of the etching solution and thus helped to adjust the etching selectivity.

[0036] As shown in Example 1, by adding thiazole as an etching inhibitor for titanium nitride, the etching rate of titanium nitride was significantly reduced, satisfying the high selectivity requirements for both silicon nitride and titanium nitride. This indicates that the etching inhibitor has a significant impact on the selectivity. In Examples 1-8, the selectivity of both silicon nitride and titanium nitride was greater than 20, thus meeting the requirements for high selectivity for both.

[0037] Analysis of experimental data from the examples and comparative examples reveals that when the etchant is a single acidic system, it is difficult to achieve high selectivity etching of different semiconductor materials on the same substrate. Therefore, to meet the etching selectivity requirements of the etchant for different substrates during chip manufacturing, additives with different functions need to be added to the original system according to actual needs. This promotes the etching of the sacrificial layer material and inhibits the etching of the protective layer material, thereby achieving high selectivity of the etchant. Furthermore, SiN requires etching in a high-temperature etchant to ensure a stable etching rate and etching amount. However, the etching rate of TiN in a high-temperature etchant is unstable, and TiN etching becomes increasingly faster. To meet the requirement of etching only the silicon nitride layer while protecting the titanium nitride layer, adding inhibitors can achieve efficient etching of SiN at high temperatures while simultaneously weakening the etching effect on TiN, thus achieving high selectivity for SiN and TiN under high-temperature etchant conditions. The above examples describe preferred embodiments of the present invention, but the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, including combinations of various technical features in any other way. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention. Therefore, the scope of protection of this invention patent shall be determined by the appended claims.

Claims

1. A high-temperature selective etching solution for silicon nitride and titanium nitride, characterized in that, The etching solution is heated to above 100°C and contains 40 wt% phosphoric acid, 3.5 wt% hydrofluoric acid, 1.0 wt% sodium phosphate, 0.05 wt% lauryl alcohol polyoxyethylene ether, 0.2 wt% 2-imidazolidineone, and the remainder is ultrapure water.

2. The etching solution according to claim 1, characterized in that: The phosphoric acid mentioned is electronic-grade phosphoric acid with a mass concentration of 70-95%.

3. The etching solution according to claim 1, characterized in that: The hydrofluoric acid is electronic-grade hydrofluoric acid with a mass concentration of 20-50%.

4. The method for preparing the etching solution according to any one of claims 1 to 3, characterized in that: During preparation, phosphoric acid, hydrofluoric acid and water are mixed in a certain proportion, and then 2-imidazolidineone, lauryl alcohol polyoxyethylene ether and sodium phosphate are added in sequence and mixed well. After sealing, it is stored for 4-8 hours to obtain the final product.

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