Buffered oxide etchant with high etching uniformity

Abstract

The application discloses a kind of buffer oxide etching solution with high etching uniformity.The main components of the etching solution are hydrofluoric acid, ammonium fluoride, corrosion inhibitor and ultrapure water.The etching solution of the application is used for etching of silicon oxide film, and has little corrosion effect on tungsten nitride layer, and the surface uniformity of tungsten nitride layer is good after etching.The corrosion inhibitor has strong coordination ability and adsorption performance, and the corrosion inhibitor and tungsten nitride surface occur chemical adsorption, forming a protective film, which can prevent the further reaction of etching solution and tungsten nitride.The etching solution of the application has high selectivity to silicon oxide layer and tungsten nitride, and the etching selectivity ratio can be >4000.The etching solution of the application can effectively inhibit the corrosion of tungsten nitride, while ensuring the surface uniformity of tungsten nitride after etching of silicon oxide.

Description

Technical Field

[0001] This invention belongs to the field of etching solution technology, specifically relating to a buffer oxide etching solution with high etching uniformity and its application. Background Technology

[0002] Silicon oxide possesses advantages such as high dielectric constant and low leakage current, making it suitable for use as the gate oxide in MOSFETs and as a dielectric layer in IC manufacturing processes. Tungsten nitride, with its high hardness, high melting point, and good chemical stability, plays a variety of roles in semiconductor devices. It can serve as the contact layer between the source and drain electrodes in transistors, and also as a metallization layer to connect different parts of a semiconductor device.

[0003] Buffered oxide etchant (BOE) is commonly used for wet etching to remove the oxide layer in the thin gate oxide region, followed by over-etching for a certain period. However, conventional BOE etchants corrode the tungsten nitride layer too quickly, resulting in poor surface uniformity after over-etching of the oxide layer, which affects subsequent film deposition processes. To address this issue, this invention introduces a corrosion inhibitor that suppresses tungsten nitride layer corrosion. This formulation exhibits excellent selectivity and improves the etching uniformity of the tungsten nitride layer. Summary of the Invention

[0004] This invention provides a buffer oxide etching solution with high etching uniformity and its preparation method. The etching solution can inhibit tungsten nitride corrosion and improve the etching uniformity of tungsten nitride.

[0005] This invention relates to a buffer oxide etching solution with high etching uniformity, wherein the etching solution comprises: 1-10% hydrofluoric acid, 18-22% ammonium fluoride, 0.02-0.2% corrosion inhibitor, and the remainder being ultrapure water.

[0006] Furthermore, the present invention relates to the above-mentioned etching solution, wherein the hydrofluoric acid is electronic grade and has a mass concentration of 48-50%.

[0007] Furthermore, the present invention relates to the above-mentioned etching solution, wherein the ammonium fluoride is electronic grade and has a mass concentration of 39-41%.

[0008] Furthermore, the present invention relates to the above-mentioned etching solution, wherein the resistivity of ultrapure water at 25°C is not less than 18 megohms.

[0009] Furthermore, the present invention relates to the above-mentioned etching solution, wherein the etching inhibitor is at least one selected from 2-amino-4-oxo-3,4-dihydropteridine-6-carboxylic acid, pteridine-4-ol, 2-amino-4-hydroxypteridine, 2-amino-4-hydroxypteridine-6-carboxylic acid, and 2,4-dihydroxypteridine.

[0010] Furthermore, this invention relates to the aforementioned etching solution, in which hydrofluoric acid is used to etch the silicon oxide layer; ammonium fluoride is used to provide fluoride ions to stabilize the etching rate of the etching solution; the corrosion inhibitor has strong coordination ability and adsorption performance, and the nitrogen atoms in the corrosion inhibitor form coordination bonds with the tungsten atoms on the tungsten nitride surface, thereby adsorbing onto the tungsten nitride surface. This chemical adsorption can effectively prevent the etching solution from contacting the tungsten nitride, thereby inhibiting the etching rate of the tungsten nitride. In addition, the adsorption of the corrosion inhibitor changes the charge distribution and chemical properties of the tungsten nitride surface, further affecting the reactivity of the etching solution with the tungsten nitride.

[0011] Furthermore, the silicon oxide thin film used in this invention is Thermal Oxide, TEOS, or BPSG.

[0012] Furthermore, the present invention relates to the aforementioned etching solution, which exhibits high selectivity for silicon oxide and tungsten nitride layers, with an etching rate selectivity ratio > 4000. Specifically, it relates to the etching of structures requiring uniformity of the tungsten nitride layer. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the silicon oxide structure sheet before etching.

[0014] Figure 2 This is a schematic diagram of the etched silicon oxide structure. Detailed Implementation

[0015] The present invention will be further illustrated by the following embodiments, but the present invention is not limited to the embodiments described.

[0016] 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, slowly stir and etch the silicon oxide thin film wafer, tungsten nitride wafer, and structural sheet into the etching solution. The thickness of the silicon oxide and tungsten nitride 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. The roughness of the tungsten nitride after etching is measured using an AFM (Anti-Factor Method). The U-value is used to determine the uniformity of the tungsten nitride etching. U = (max - min) / (2 * average).

[0017] Example 1

[0018] Composition of Example 1: 7% hydrofluoric acid, 20% ammonium fluoride, 0.12% 2-amino-4-hydroxypteridine, balance water.

[0019] Example 2

[0020] Composition of Example 2: 7% hydrofluoric acid, 20% ammonium fluoride, 0.02% 2-amino-4-oxo-3,4-dihydropteridine-6-carboxylic acid, balance water.

[0021] Example 3

[0022] The composition of Example 3: 7% hydrofluoric acid, 20% ammonium fluoride, 0.07% 2,4-dihydroxypteridine, and the balance being water.

[0023] Example 4

[0024] The composition of Example 4: 7% hydrofluoric acid, 20% ammonium fluoride, 0.15% 2-amino-4-hydroxypteridine, and the balance being water.

[0025] Example 5

[0026] The composition of Example 5: 7% hydrofluoric acid, 20% ammonium fluoride, 0.2% 2-amino-4-hydroxypteridine, and the balance being water.

[0027] Example 6

[0028] The composition of Example 6: 7% hydrofluoric acid, 20% ammonium fluoride, 0.1% pteridine-4-ol, and the balance being water.

[0029] Example 7

[0030] The composition of Example 7: 4% hydrofluoric acid, 20% ammonium fluoride, 0.12% 2-amino-4-hydroxypteridine-6-carboxylic acid, and the balance being water.

[0031] Example 8

[0032] The composition of Example 8 is: 10% hydrofluoric acid, 20% ammonium fluoride, 0.08% 2-amino-4-hydroxypteridine-6-carboxylic acid, and the balance is water.

[0033] Comparative Example 1

[0034] The composition of Comparative Example 1: 7% hydrofluoric acid, 20% ammonium fluoride, and the balance being water.

[0035] Comparative Example 2

[0036] The composition of Comparative Example 2 was: 7% hydrofluoric acid, 20% ammonium fluoride, 0.01% 2-amino-4-hydroxypteridine, and the balance being water.

[0037] Comparative Example 3

[0038] The composition of Comparative Example 3 was: 7% hydrofluoric acid, 20% ammonium fluoride, 0.3% 2-amino-4-hydroxypteridine, and the balance being water.

[0039] Comparative Example 4

[0040] The composition of Comparative Example 4: 7% hydrofluoric acid, 20% ammonium fluoride, 0.12% 2-pyridinecarboxylic acid, and the balance being water.

[0041] Comparative Example 5

[0042] The composition of Comparative Example 5 was: 7% hydrofluoric acid, 20% ammonium fluoride, 0.12% 4,6-diaminopyrimidine, and the balance being water.

[0043] Comparative Example 6

[0044] The composition of Comparative Example 6 was: 7% hydrofluoric acid, 20% ammonium fluoride, 0.12% 5-hydroxyquinoline, and the balance being water.

[0045] Table 1. Etching rate, etch selectivity, U value, Ra of tungsten nitride after etching, and properties of the etching solution.

[0046]

[0047] As shown in the table, the etching solutions in Examples 1-8 were all in a clear state. The etching solutions had a significant inhibitory effect on tungsten nitride, with an etching rate selectivity ratio of silicon dioxide to tungsten nitride > 4000. The tungsten nitride exhibited excellent uniformity after etching (U values ​​all below 1.2%) and low roughness (Ra values ​​all below 0.14 nm). The examples show that when the amount of corrosion inhibitor added is around 0.12%, the etching solution has the best inhibitory effect on tungsten nitride, the highest etching rate selectivity ratio of silicon dioxide to tungsten nitride, and the best uniformity after tungsten nitride etching. Comparative Example 1 did not contain a corrosion inhibitor, resulting in a fast etching rate for tungsten nitride, but poor uniformity and high roughness after etching. Comparative Example 2 contained a small amount of corrosion inhibitor, resulting in a low etching rate selectivity ratio, and the tungsten nitride etching uniformity was better than that of Comparative Example 1. Comparative Example 3 contained an excessive amount of corrosion inhibitor, resulting in a high etching rate selectivity ratio, but the solution was turbid, and the uniformity after tungsten nitride etching was poor. In Comparative Examples 4-6, the corrosion inhibitors were changed. It can be seen that other heterocyclic compounds have little effect on inhibiting tungsten nitride etching, and the tungsten nitride has poor uniformity and large roughness after etching.

[0048] Obviously, the above embodiments and comparative examples are merely for illustrative purposes and are not intended to limit the implementation. Figure 1 The illustration shows a schematic diagram of a silicon dioxide structure. The etching solution is also applicable to different processes where the silicon dioxide layer requires a high etch selectivity for tungsten nitride. Those skilled in the art will recognize that various variations or modifications can be made based on the above description; it is neither necessary nor possible to exhaustively list all possible implementations. However, any obvious variations or modifications derived therefrom are still within the scope of this invention.

Claims

1. A buffered oxide etching solution with high etching uniformity, characterized in that, The etching solution comprises 1-10% hydrofluoric acid, 18-22% ammonium fluoride, 0.02-0.2% corrosion inhibitor, and the remainder is ultrapure water. The corrosion inhibitor is selected from at least one of 2-amino-4-oxo-3,4-dihydropteridine-6-carboxylic acid, pteridine-4-ol, 2-amino-4-hydroxypteridine, 2-amino-4-hydroxypteridine-6-carboxylic acid, and 2,4-dihydroxypteridine.

2. The buffer oxide etching solution with high etching uniformity according to claim 1, characterized in that, The hydrofluoric acid in the etching solution is electronic grade, with a mass concentration of 48-50%.

3. The buffer oxide etching solution with high etching uniformity according to claim 1, characterized in that, The ammonium fluoride in the etching solution is electronic grade, with a mass concentration of 39-41%.

4. The buffer oxide etching solution with high etching uniformity according to claim 1, characterized in that, The resistivity of the ultrapure water at 25°C is not less than 18 megohms.

5. The application of a buffered oxide etchant with high etching uniformity as described in any one of claims 1-4 in the etching of silicon oxide thin films.

6. The application according to claim 5, characterized in that: The etching temperature is 25℃±5℃.

7. The application according to claim 5, characterized in that: The silicon oxide film includes any one of Thermal Oxide, TEOS, or BPSG.

8. The application of a buffer oxide etchant with high etching uniformity as described in any one of claims 1-4 for selective etching of silicon oxide layers and tungsten nitride thin films, wherein the etching rate selectivity ratio is >4000.

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