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

Abstract

The invention relates to the technical field of semiconductors and electronic chemicals, and particularly discloses an etching solution for selectively etching silicon nitride and titanium nitride and a preparation method of the etching solution, the etching solution comprises 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 agent, 0.01-1.8% of a solubilizer, 0.1-7% of an etching inhibitor and the balance of water. Wherein the pH buffering agent can effectively stabilize the pH of the etching solution, and the solubilizer can improve the solubility of a solvent in the etching solution, reduce the tension of a solid-liquid phase interface in the solution and promote the transfer rate of interphase substances; the etching inhibitor and metal can form a layer of film on the surface of titanium nitride in a coordination bond mode, and it is guaranteed that silicon nitride and titanium nitride have the high selection ratio. The etching solution provided by the invention can inhibit the etching rate of titanium nitride under the condition of higher etching rate of silicon nitride, and can ensure that the requirement of high selection ratio of silicon nitride and titanium nitride is met.

Description

Technical Field

[0001] The invention belongs to the technical field of electronic chemicals, and in particular relates to an etching solution for selectively etching silicon nitride and titanium nitride and a preparation method thereof. Background Art

[0002] Silicon nitride has excellent thermal stability, mechanical properties and chemical stability, and is widely used in high-temperature, high-power and high-frequency electronic devices. It has a wide energy gap and its conductivity can be adjusted by doping, so it is regarded as an important semiconductor material. Titanium nitride has good metal diffusion barrier properties and low resistivity after annealing. It also has many applications in the semiconductor industry, such as hard masks, metal barrier layers, conductive electrodes, metal gates, etc.; in addition, titanium nitride is also used in advanced process chips to improve the performance of transistors.

[0003] The semiconductor industry has developed rapidly in recent years. With the continuous reduction of semiconductor devices and feature sizes, it is necessary to improve and perfect the current semiconductor manufacturing methods and processes. Etching technology has been used by the industry for a long time as the most stable, effective and widely used technology for semiconductor materials. In the etching process, it is necessary 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 etching selectivity ratio. The higher this ratio is, the more conducive it is to improving the product yield. However, as the semiconductor industry has higher and higher requirements for product yield, how to increase the etching rate of the etching solution on silicon nitride while minimizing the etching of the barrier layer titanium nitride has become a problem that needs to be solved urgently in this field.

[0004] CN 113604803 A discloses an etching solution for selectively etching tungsten and titanium nitride, which includes hydrogen peroxide, hydrogen peroxide stabilizer, nitric acid, organic acid, etching inhibitor, surfactant and deionized water. The etching solution is used to etch tungsten and titanium nitride at 50°C. The results show that the etching solution can etch metal tungsten at a higher rate and can inhibit the etching rate of titanium nitride in the etching solution, thereby maintaining a higher selectivity. CN117720925A discloses a groove buffer etching solution for inhibiting the corrosion of titanium nitride, the main components of which are hydrofluoric acid, ammonium fluoride, organic amine, surfactant and ultrapure water. The etching solution is used to etch silicon oxide and titanium nitride at 25°C. The results show that the etching solution has a higher selectivity for silicon oxide layer and titanium nitride layer. While etching the silicon oxide groove cleanly without residue, the corrosion of the titanium nitride layer can be slowed down, achieving etching of the groove structure requiring a high selectivity. Although the etching inhibitors currently used can slow down the etching rate of titanium nitride in the acidic etching solution system to a certain extent, as the semiconductor process gradually increases from 28nm to 14nm and 7nm, the semiconductor industry has higher requirements for the etching rate of titanium nitride in the acidic etching solution system. And because the silicon nitride described in the present invention has the characteristics of stable chemical properties, it requires a high-temperature acidic solution above 100°C to achieve rapid etching. Therefore, it is particularly urgent to develop a high-selectivity etching solution with excellent comprehensive performance. Summary of the invention

[0005] The present invention provides an etching solution for selectively etching silicon nitride and titanium nitride and a preparation method thereof. The etching solution can efficiently etch silicon nitride under high temperature conditions above 100°C, and can inhibit the chemical corrosion and electrochemical corrosion of the etching solution on titanium nitride, greatly slowing 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 of 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, wherein the etching solution contains the following components in 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, and the balance is water.

[0007] In some of the 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 embodiments, the pH buffer is one or a combination of ammonium tartrate, sodium oxalate, sodium phosphate, sodium acetate and hexamethylenetetramine.

[0009] In some embodiments, the solubilizer is one or a combination 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 embodiments, the etching inhibitor is one or a combination 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 the embodiments, the water is ultrapure water.

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

[0013] The present invention also relates to a method for preparing the etching solution. During the preparation, phosphoric acid, hydrofluoric acid and water are mixed in proportion, and then an etching inhibitor, a solubilizing agent and a pH buffer are added in sequence and mixed, and the etching solution is sealed and stored for 4 to 8 hours.

[0014] The present invention has the following beneficial effects: 1. Compared with the existing etching process, the present invention provides an etching solution for selectively etching silicon nitride and titanium nitride. While ensuring that the etching solution can quickly etch silicon nitride under high temperature conditions above 100°C, the chemical corrosion and electrochemical corrosion of titanium nitride by the etching solution are suppressed, the etching rate of titanium nitride in the high temperature etching solution is greatly slowed down, and the etching stability and uniformity can be achieved.

[0015] 2. The solubilizing agent in the etching solution of the present 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 the interphase material, 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 protection layer on the surface of titanium nitride in the form of a coordination bond with the metal, which greatly reduces the etching rate of the etching solution on titanium nitride and ensures that silicon nitride and titanium nitride have a high etching selectivity ratio. DETAILED DESCRIPTION

[0017] The present invention is described in detail below in conjunction with specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and a specific operation process, but the protection scope 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: 40wt% phosphoric acid, 4.5wt% hydrofluoric acid, 1.5wt% sodium oxalate, 0.1wt% polyacrylamide, 0.1wt% thiazole, and the rest are ultrapure water.

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

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

[0021] Example 4 An etching solution for selectively etching silicon nitride and titanium nitride, comprising: 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 rest are ultrapure water.

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

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

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

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

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

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

[0028] Comparative Example 3 An etching solution comprises the following: 45wt% phosphoric acid, 4wt% hydrofluoric acid, 0.1wt% sodium oxalate, 2.5wt% polyacrylamide, and the rest is ultrapure water.

[0029] Comparative Example 4 An etching solution comprises the following components: 40wt% phosphoric acid and 3.5wt% hydrofluoric acid, and the rest is ultrapure water.

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

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

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

[0033] The etching solutions in the above embodiments and comparative examples were used to etch the silicon nitride and titanium nitride samples. Specifically, the cut silicon nitride and titanium nitride samples were cleaned and dried, and the initial thickness of silicon nitride and titanium nitride were measured using an ellipsometer and a four-probe thickness gauge, respectively. The samples were then fixed with etching brackets, placed in an etching solution at 100°C for etching for 10 minutes, and then taken out and cleaned with ultrapure water at 70°C for 10 seconds, and then dried with nitrogen. The thickness of silicon nitride and titanium nitride after etching was tested, and the corresponding etching rate was calculated by comparing the change in the thickness of the samples before and after etching. The details are shown in Table 1 below.

[0034] Table 1

[0035] It can be seen from the data in the table that in Comparative Example 1, no pH buffer, solubilizer and etching inhibitor were added, the etching rates of silicon nitride and titanium nitride were unstable, the etching rate of titanium nitride gradually increased with time, and the etching rate was high, resulting in a low etching selectivity. In Comparative Example 2, sodium oxalate was added as a pH buffer, which effectively alleviated the problem of unstable etching rate, 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 can increase the wettability of the etching solution, thereby facilitating the adjustment of the etching selectivity.

[0036] As can be seen from Example 1, by adding thiazole as an etching inhibitor for titanium nitride, the etching rate of titanium nitride is greatly reduced, and the high selectivity of silicon nitride and titanium nitride is met, which shows that the etching inhibitor has a greater impact on the selectivity. The selectivity of silicon nitride and titanium nitride in Examples 1-8 is greater than 20, which can meet the requirements of high selectivity of silicon nitride and titanium nitride.

[0037] By analyzing the experimental data of the embodiments and comparative examples, it can be known that when the etching solution is a single acidic system, it is difficult to achieve high selectivity etching for different semiconductor materials of the same substrate. Therefore, in order to meet the etching selectivity of the etching solution for different substrates in the chip manufacturing process, it is necessary to add additives with different functions to the original system according to actual needs, and promote the etching of the sacrificial layer material and inhibit the etching of the protective layer material, so as to achieve a high selectivity of the etching solution. Moreover, SiN needs to be etched in a high-temperature etching solution to ensure a stable etching rate and etching amount. However, the etching rate of TiN in a high-temperature etching solution is unstable, and TiN etching will become faster and faster. In order to meet the needs of etching only the silicon nitride layer and protecting the titanium nitride layer, the etching solution can be added by adding an inhibitor to meet the high-efficiency etching of SiN at high temperature, while weakening the etching effect of the etching solution on TiN, so as to achieve a high selectivity of SiN and TiN under high-temperature etching solution conditions. The above embodiments describe the preferred embodiments of the present invention, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical scheme of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other way, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention, and all belong to the protection scope of the present invention. Therefore, the protection scope of the patent for this invention shall be based on the attached claims.

Claims

1. An etching solution for selectively etching silicon nitride and titanium nitride, characterized in that: 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 pH buffer, 0.01-1.8% of solubilizer and 0.1-7% of etching inhibitor, and the balance is water.

2. The etching solution according to claim 1, characterized in that: The phosphoric acid 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 etching solution according to claim 1, characterized in that: The pH buffer is one or a combination of ammonium tartrate, sodium oxalate, sodium phosphate, sodium acetate and hexamethylenetetramine.

5. The etching solution according to claim 1, characterized in that: The solubilizer is one of polyethylene glycol 400, polyethylene glycol 600, sodium lauryl sulfate, polyacrylamide, octadecyl vinyl ether, diethyl phosphate, triethanolamine, nonylphenol polyoxyethylene ether and lauryl alcohol polyoxyethylene ether, or a combination of several of them.

6. The etching solution according to claim 1, characterized in that: The etching inhibitor is one or a combination of thiazole, 2-amino-1,3,4-thiadiazole, 2,2-bipyridine, 2-mercaptoimidazole, 4-pyridine, imidazoline, 2-aminopyridine, 2-imidazolidinone and benzotriazole.

7. The etching solution according to claim 1, characterized in that: The water is ultrapure water.

8. The etching solution according to any one of claims 1 to 7, characterized in that: In the etching solution, the pH buffer is sodium phosphate, the solubilizer is lauryl alcohol polyoxyethylene ether and the etching inhibitor is 2-imidazolidinone.

9. The method for preparing the etching solution according to any one of claims 1 to 8, characterized in that: During preparation, phosphoric acid, hydrofluoric acid and water are mixed in proportion, and then an etching inhibitor, a solubilizing agent and a pH buffer are added in sequence and mixed, and the mixture is sealed and stored for 4 to 8 hours.

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