Buffer oxide etching solution with high etching uniformity

Abstract

The invention discloses a buffer oxide etching solution with high etching uniformity. The etching solution mainly comprises hydrofluoric acid, ammonium fluoride, a corrosion inhibitor and ultrapure water. The etching solution provided by the invention is used for etching a silicon oxide film, and has a small corrosion effect on a tungsten nitride layer, and the surface uniformity of the tungsten nitride layer after etching is completed is good. The corrosion inhibitor has relatively strong coordination capability and adsorption performance, and the corrosion inhibitor and the surface of tungsten nitride are subjected to chemical adsorption to form a layer of protective film, so that further reaction between the etching liquid and tungsten nitride can be prevented. The etching solution provided by the invention has high selectivity to a silicon oxide layer and tungsten nitride, and the etching selection ratio can be greater than 4000. The etching solution provided by the invention can effectively inhibit corrosion of tungsten nitride, and ensures the uniformity of the surface of tungsten nitride after silicon oxide etching is completed at the same time.

Description

Technical Field

[0001] The invention belongs to the technical field of etching solutions, and in particular relates to a buffered oxide etching solution with high etching uniformity and application thereof. Background Art

[0002] Silicon oxide has the advantages of high dielectric constant and low leakage current. It can be used as gate oxide in MOSFET in semiconductor process and as dielectric layer in IC process. Tungsten nitride has high hardness, high melting point and good chemical stability. It can play a variety of roles in semiconductor devices. Tungsten nitride can be used as contact layer of source and drain in transistor. Tungsten nitride can also be used as metallization layer to connect different parts of semiconductor devices.

[0003] Buffered oxide etchant (BOE) is often used for wet etching to remove the oxide layer in the thin gate oxide area and over-etch the surface for a certain period of time. Conventional BOE etching solution corrodes the tungsten nitride layer too quickly, and the surface uniformity of the tungsten nitride is poor after the oxide layer is over-etched, which will affect the subsequent film forming process. In order to solve this problem, the present invention introduces a corrosion inhibitor that can inhibit the corrosion of the tungsten nitride layer. The formula has excellent selectivity and can improve the etching uniformity of tungsten nitride. Summary of the invention

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

[0005] The invention relates to a buffered oxide etching solution with high etching uniformity. The etching solution comprises: 1-10% of hydrofluoric acid, 18-22% of ammonium fluoride, 0.02-0.2% of a corrosion inhibitor, and the remainder is 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 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 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 corrosion 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, the present invention relates to the above-mentioned etching solution, wherein hydrofluoric acid is used to etch the silicon oxide layer; ammonium fluoride is used to provide fluorine 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 surface of tungsten nitride, thereby adsorbing on the surface of tungsten nitride. This chemical adsorption can effectively prevent the contact between the etching solution and tungsten nitride, thereby inhibiting the etching rate of tungsten nitride. In addition, the adsorption of the corrosion inhibitor changes the charge distribution and chemical properties on the surface of tungsten nitride, further affecting the reaction activity of the etching solution and tungsten nitride.

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

[0012] Furthermore, the present invention relates to the above etching solution, which has high selectivity to silicon oxide layer and tungsten nitride layer, and the etching rate selectivity ratio is greater than 4000. Specifically, it relates to structural etching with uniformity requirement for tungsten nitride layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Schematic diagram of a silicon oxide structure before etching.

[0014] Figure 2 Schematic diagram of the silicon oxide structure after etching. DETAILED DESCRIPTION

[0015] The present invention is further described below by way of examples, but the present invention is not limited to the examples.

[0016] First, prepare the etching solution according to the composition, stir and mix for 60 minutes, put the PFA bottle containing the etching solution into a low-temperature thermostatic bath (25°C) for 3 hours, and slowly stir and etch the silicon oxide film wafer, tungsten nitride wafer, and structural wafer into the etching solution. The thickness of silicon oxide and tungsten nitride wafers was detected by ellipsometer before and after etching, and the corresponding etching rate was calculated according to the thickness difference before and after etching / etching time. The roughness of tungsten nitride after etching was measured by AFM. The U value is used to determine the uniformity of tungsten nitride etching. U=(max-min) / (2*average).

[0017] Example 1 The composition of Example 1: 7% hydrofluoric acid, 20% ammonium fluoride, 0.12% 2-amino-4-hydroxypteridine, and the balance is water.

[0018] Example 2 The composition of Example 2: 7% hydrofluoric acid, 20% ammonium fluoride, 0.02% 2-amino-4-oxo-3,4-dihydropteridine-6-carboxylic acid, and the balance is water.

[0019] Example 3 The composition of Example 3: 7% hydrofluoric acid, 20% ammonium fluoride, 0.07% 2,4-dihydroxypteridine, and the balance is water.

[0020] Example 4 The composition of Example 4: 7% hydrofluoric acid, 20% ammonium fluoride, 0.15% 2-amino-4-hydroxypteridine, and the balance is water.

[0021] Example 5 The composition of Example 5: 7% hydrofluoric acid, 20% ammonium fluoride, 0.2% 2-amino-4-hydroxypteridine, and the balance is water.

[0022] Example 6 The composition of Example 6: 7% hydrofluoric acid, 20% ammonium fluoride, 0.1% pteridine-4-ol, and the balance is water.

[0023] Example 7 The composition of Example 7: 4% hydrofluoric acid, 20% ammonium fluoride, 0.12% 2-amino-4-hydroxypteridine-6-carboxylic acid, and the balance is water.

[0024] Example 8 The composition of Example 8: 10% hydrofluoric acid, 20% ammonium fluoride, 0.08% 2-amino-4-hydroxypteridine-6-carboxylic acid, and the balance is water.

[0025] Comparative Example 1 The composition of Comparative Example 1: 7% hydrofluoric acid, 20% ammonium fluoride, and the balance water.

[0026] Comparative Example 2 The composition of Comparative Example 2: 7% hydrofluoric acid, 20% ammonium fluoride, 0.01% 2-amino-4-hydroxypteridine, and the balance is water.

[0027] Comparative Example 3 The composition of Comparative Example 3: 7% hydrofluoric acid, 20% ammonium fluoride, 0.3% 2-amino-4-hydroxypteridine, and the balance is water.

[0028] Comparative Example 4 The composition of Comparative Example 4: 7% hydrofluoric acid, 20% ammonium fluoride, 0.12% 2-picolinic acid, and the balance is water.

[0029] Comparative Example 5 The composition of Comparative Example 5: 7% hydrofluoric acid, 20% ammonium fluoride, 0.12% 4,6-diaminopyrimidine, and the balance water.

[0030] Comparative Example 6 The composition of Comparative Example 6: 7% hydrofluoric acid, 20% ammonium fluoride, 0.12% 5-hydroxyquinoline, and the balance water.

[0031] Table 1. Etching rate, etching selectivity, U value, Ra of tungsten nitride after etching, and properties of etching solution

[0032] As can be seen from the table, the etching solutions in Examples 1-8 are all in a clear state, and the etching solutions have a significant inhibitory effect on tungsten nitride. The etching rate selectivity of silicon dioxide and tungsten nitride is greater than 4000, and the uniformity of tungsten nitride after etching is excellent (U values ​​are all less than 1.2%) and the roughness is small (Ra values ​​are all less than 0.14nm). It can be seen from the examples that the amount of corrosion inhibitor added is about 0.12%, the etching solution has the best inhibitory effect on tungsten nitride, the etching rate selectivity of silicon dioxide and tungsten nitride is the highest, and the uniformity of tungsten nitride after etching is the best. Comparative Example 1 does not contain a corrosion inhibitor, and the etching rate of tungsten nitride is fast. The uniformity of tungsten nitride after etching is poor and the roughness is large. Comparative Example 2 contains a small amount of corrosion inhibitor, the etching rate selectivity is low, and the etching uniformity of tungsten nitride is better than that of Comparative Example 1. Comparative Example 3 contains an excessive amount of corrosion inhibitor, the etching rate selectivity is high, but the solution is turbid, and the uniformity of tungsten nitride after etching is poor. In Comparative Examples 4-6, the corrosion inhibitor was replaced, and it can be seen that other heterocyclic compounds have no obvious inhibitory effect on tungsten nitride etching, and the tungsten nitride has poor uniformity and large roughness after etching.

[0033] Obviously, the above embodiments and comparative examples are merely examples for the purpose of illustrating clearly, and are not intended to limit the implementation methods. Figure 1 The schematic diagram of the silicon oxide structure is shown in FIG. 1 . The etching solution is also applicable to different processes that require a high etching selectivity ratio of the silicon dioxide layer to tungsten nitride. For technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the protection scope of the 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.

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

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

4. The buffered 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 buffered oxide etching solution with high etching uniformity according to claim 1, characterized in that: The corrosion 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.

6. Use of the buffered oxide etching solution with high etching uniformity as claimed in any one of claims 1 to 5 in etching silicon oxide films.

7. The use according to claim 6, characterized in that: The etching temperature is 25°C±5°C.

8. The use according to claim 6, characterized in that: The silicon oxide film includes any one of Thermal Oxide, TEOS, or BPSG.

9. Use of the buffered oxide etching solution with high etching uniformity as claimed in any one of claims 1 to 5 for selectively etching a silicon oxide layer in thin film etching of a silicon oxide layer and a tungsten nitride layer, wherein the etching rate selectivity ratio is greater than 4000.

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