A highly selective and low-foaming etchant

Abstract

The invention discloses a highly selective and low-foaming buffered oxide etching solution. The etching solution mainly comprises hydrofluoric acid, ammonium fluoride, additives, surfactants and ultrapure water. The etching solution of the invention is used for etching silicon dioxide thin films, and can simultaneously inhibit etching of polysilicon layers and silicon nitride layers. The additive can simultaneously inhibit etching of polysilicon layers and silicon nitride layers, and has good dispersibility and is not easy to foam in the solution system, thereby avoiding uneven etching process. The surfactant is mainly used to reduce the surface tension of the etching solution and improve the wettability of the etching solution. The etching solution of the invention has high selectivity for silicon dioxide layers and polysilicon layers; at the same time, it has high selectivity for silicon dioxide layers and silicon nitride layers, and the etching rate selectivity ratio is ≥12. The etching solution of the invention can adjust the content of each component to meet the etching selectivity ratio requirements of silicon dioxide layers to polysilicon layers and silicon nitride layers in different processes.

Description

Technical Field

[0001] The present invention relates to a highly selective and low-foaming buffered oxide etching solution in the semiconductor manufacturing industry, which can rapidly etch silicon oxide films while inhibiting etching of polysilicon layers and silicon nitride layers, and more specifically to a trench structure etching solution with high selectivity requirements. Background Art

[0002] Wet electronic chemicals are key basic chemical materials in integrated circuits. They are various liquid chemical materials used in wet processes of microelectronics and optoelectronics (mainly including wet etching, cleaning, developing, stripping, etc.), and are one of the important wafer manufacturing materials. The silicon dioxide layer can be used as a protective layer or gate oxide layer for MOS devices; the interface characteristics between polysilicon and silicon dioxide are excellent, and a specific resistance can be obtained through doping, so it can be used as a gate electrode; silicon nitride can effectively inhibit the diffusion of impurities and moisture, and can be used as a passivation protective layer. In the etching or cleaning process, the electronic chemicals used must ensure that there is no residue in the etching of silicon dioxide, while causing as little corrosion to polysilicon and silicon nitride as possible.

[0003] Buffered oxide etchant (BOE) is usually used for silicon dioxide etching, and its main components are HF, NH4F and water. Conventional BOE etching solution often has a faster etching rate for polysilicon and silicon nitride layers, which cannot meet the high selectivity requirements of advanced processes. The additives introduced in the present invention to improve the selectivity can simultaneously inhibit the corrosion of polysilicon and silicon nitride layers, and have good dispersibility and are not easy to foam in the system. In addition, a surfactant is introduced to reduce the surface tension of the etching solution and improve the wettability of the etching solution. This formula has excellent selectivity and can meet the process requirements of high-end processes. Summary of the invention

[0004] The present invention provides a highly selective and low-foaming buffered oxide etching solution and a preparation method thereof. The etching solution can quickly etch a silicon oxide film while protecting a polysilicon layer and a silicon nitride layer, thereby meeting the etching selectivity requirements of a silicon dioxide layer to a polysilicon layer and a silicon nitride layer in different processes.

[0005] The invention relates to a high-selectivity and low-foam etching solution, which comprises: 1-15% of hydrofluoric acid, 10-25% of ammonium fluoride, 0.01-0.3% of additives, 0.05-0.5% of surfactant, and the rest is ultrapure water.

[0006] Furthermore, the present invention relates to the above 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 38-41%.

[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 additive is at least one selected from poly(4-vinylpyridine toluenesulfonate), sodium polyanissulfonate, poly(4-styrenesulfonic acid), potassium polydivinylsulfonate, and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid).

[0010] Furthermore, the present invention relates to the above etching solution, wherein the surfactant is any one selected from alkoxy polyethylene hydroxyethanol, N-ethyl perfluorooctane sulfonamide ethanol, and ethoxylated-C12-18-alcohol.

[0011] Furthermore, the present invention relates to the above-mentioned etching solution, wherein hydrofluoric acid is used for etching a silicon dioxide film; ammonium bifluoride is used for providing fluoride ions to stabilize the etching rate of the etching solution; the additive can simultaneously inhibit the etching of a polysilicon layer and a silicon nitride layer, and has good dispersibility and is not prone to foaming in the solution system, so that the wafer surface is etched flat; and the surfactant is mainly used for reducing the surface tension of the etching solution, improving the wettability of the etching solution, and reducing the surface roughness of the wafer.

[0012] Furthermore, the present invention relates to the above etching solution, and the surface tension range is 20-35 mN / m (25° C.).

[0013] Furthermore, the silicon dioxide film used in the present invention is thermal silicon dioxide; the polysilicon used is of two types: doped (D-Poly) and undoped (U-Poly).

[0014] Furthermore, the present invention relates to the above-mentioned etching solution, which has high selectivity for the silicon dioxide layer and D-Poly, and the etching rate selection ratio is ≥350; the etching solution has high selectivity for the silicon dioxide layer and U-Poly, and the etching rate selection ratio is ≥1000; the etching solution has high selectivity for the silicon dioxide layer and the silicon nitride layer, and the etching rate selection ratio is ≥12.

[0015] Furthermore, the present invention relates to the above-mentioned etching solution, and specifically to a trench structure etching with high selectivity requirements, and is also applicable to different processes with high etching selectivity requirements for silicon dioxide layers to polysilicon layers and silicon nitride layers. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of etching a trench structure with high selectivity requirements. DETAILED DESCRIPTION

[0017] The present invention is further described below by way of examples, but the present invention is not limited to the examples.

[0018] First, prepare the etching solution according to the composition, stir and mix for 30 minutes, then put the PFA bottle containing the etching solution into a low-temperature thermostat (25°C), and when the temperature of the etching solution is consistent with that of the low-temperature thermostat, put the silicon dioxide film wafer, silicon nitride film wafer, D-Poly wafer, and U-Poly wafer into the etching solution and let them etch. Before and after etching, use an ellipsometer to detect the thickness of the silicon dioxide film wafer, silicon nitride film wafer, D-Poly wafer, and U-Poly wafer, and calculate the corresponding etching rate according to the thickness difference before and after etching / etching time.

[0019] Surface tension test: Test the surface tension of the etching solution at 25°C.

[0020] Defoaming test experimental process: 20mL of etching solution is placed in a 100mL plastic tube, vertically shaken for 30s, and the foam height is measured after stopping for 5s.

[0021] Example 1

[0022] The composition of Example 1: 4.0 wt% hydrofluoric acid, 20 wt% ammonium fluoride, 0.05 wt% poly(4-styrene sulfonic acid), 0.1% N-ethylperfluorooctanesulfonamide ethanol, and the balance is water.

[0023] Example 2

[0024] The composition of Example 2: 6.0 wt% hydrofluoric acid, 20 wt% ammonium fluoride, 0.08 wt% poly(4-styrene sulfonic acid), 0.1% N-ethylperfluorooctanesulfonamide ethanol, and the balance is water.

[0025] Example 3

[0026] The composition of Example 3: 8.0 wt% hydrofluoric acid, 20 wt% ammonium fluoride, 0.08 wt% poly(4-styrene sulfonic acid), 0.1% N-ethylperfluorooctanesulfonamide ethanol, and the balance is water.

[0027] Example 4

[0028] The composition of Example 4: 8.0 wt% hydrofluoric acid, 20 wt% ammonium fluoride, 0.15 wt% poly (4-vinylpyridine p-toluenesulfonate), 0.2% alkoxy polyethylene hydroxyethanol, and the balance is water.

[0029] Example 5

[0030] The composition of Example 5: 8.0 wt% hydrofluoric acid, 20 wt% ammonium fluoride, 0.2 wt% poly(4-styrene sulfonic acid), 0.3% N-ethylperfluorooctanesulfonamide ethanol, and the balance is water.

[0031] Example 6

[0032] The composition of Example 6: 4.0 wt% hydrofluoric acid, 20 wt% ammonium fluoride, 0.3 wt% poly (4-vinylpyridine p-toluenesulfonate), 0.5 wt% alkoxy polyethylene hydroxyethanol, and the balance is water.

[0033] Example 7

[0034] The composition of Example 7: 8.0 wt% hydrofluoric acid, 20 wt% ammonium fluoride, 0.3 wt% poly (4-vinylpyridine p-toluenesulfonate), 0.5 wt% alkoxy polyethylene hydroxyethanol, and the balance is water.

[0035] Example 8

[0036] The composition of Example 8: 6 wt% hydrofluoric acid, 20 wt% ammonium fluoride, 0.01 wt% poly(4-vinylpyridine p-toluenesulfonate), 0.05 wt% alkoxy polyethylene hydroxyethanol, and the balance is water.

[0037] Example 9

[0038] The composition of Example 9: 8.0 wt% hydrofluoric acid, 20 wt% ammonium fluoride, 0.01 wt% poly(4-vinylpyridine p-toluenesulfonate), 0.05 wt% alkoxy polyethylene hydroxyethanol, and the balance is water.

[0039] Comparative Example 1

[0040] The composition of Comparative Example 1: 4.0 wt % hydrofluoric acid, 20 wt % ammonium fluoride, and the balance water.

[0041] Comparative Example 2

[0042] The composition of Comparative Example 2: 8.0 wt% hydrofluoric acid, 20 wt% ammonium fluoride, 0.06 wt% poly(4-vinylpyridine p-toluenesulfonate), and the balance is water.

[0043] Comparative Example 3

[0044] The composition of Comparative Example 3 is: 8.0 wt % hydrofluoric acid, 20 wt % ammonium fluoride, 0.2 wt % alkoxy polyethylene hydroxyethanol, and the balance is water.

[0045] Comparative Example 4

[0046] The composition of Comparative Example 4 is as follows: 8.0 wt% hydrofluoric acid, 20 wt% ammonium fluoride, 0.003 wt% poly(4-styrene sulfonic acid), 0.25 wt% alkoxy polyethylene hydroxyethanol, and the balance is water.

[0047] Comparative Example 5

[0048] The composition of Comparative Example 5: 8.0 wt% hydrofluoric acid, 20 wt% ammonium fluoride, 0.1 wt% poly(4-styrene sulfonic acid), 0.01 wt% ethoxylated-C12-18-alcohol, and the balance is water.

[0049] Comparative Example 6

[0050] The composition of Comparative Example 6: 4 wt% hydrofluoric acid, 20 wt% ammonium fluoride, 0.5 wt% poly(4-vinylpyridine p-toluenesulfonate), 1 wt% ethoxylated-C12-18-alcohol, and the balance is water.

[0051] Comparative Example 7

[0052] The composition of Comparative Example 7 is: 6 wt% hydrofluoric acid, 20 wt% ammonium fluoride, 0.002 wt% poly(4-vinylpyridine p-toluenesulfonate), 0.01 wt% ethoxylated-C12-18-alcohol, and the balance is water.

[0053] Table 1. Etching liquid properties, surface tension, and foam height

[0054]

[0055]

[0056] Table 2. Etching rate, etching selectivity

[0057]

[0058] It can be seen from Table 1 that the surface tension of the etching solution in Examples 1-9 is within the range of 20-35 mN / m, the etching solutions are all in a clear state, and the foam height is below 0.2 cm. It can be seen from Table 2 that in Examples 1-9, the etching solution has a significant inhibitory effect on D-Poly, U-Poly, and silicon nitride layers, and the etching rate selectivity ratio of the silicon dioxide layer to the D-Poly is ≥350; the etching rate selectivity ratio of the silicon dioxide layer to the U-Poly is ≥1000; the etching rate selectivity ratio of the silicon dioxide layer to the silicon nitride is ≥12. Comparative Example 1 does not contain additives and surfactants, and its surface tension is large. The etching rate of D-Poly, U-Poly, and silicon nitride layers is fast, and the etching rate selectivity ratio is low. Comparative Example 2 does not contain a surfactant, and the surface tension is large, but it has an inhibitory effect on the etching of D-Poly, U-Poly, and silicon nitride layers, and the etching rate selectivity ratio is high. Comparative Example 3 does not contain additives, and the surface tension is low, but it has no inhibitory effect on the etching of D-Poly, U-Poly, and silicon nitride layers. In Comparative Examples 4-7, when the surfactant is too low, the surface tension is not significantly reduced; when the additive content is too low, the inhibitory effect on the etching of D-Poly, U-Poly, and silicon nitride layers is weakened, and when the additive is excessive, the solution is turbid, which will cause particle contamination of the wafer.

[0059] 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 above is a schematic diagram of etching a trench structure with high selectivity requirements. The etching solution is also applicable to different processes with high etching selectivity requirements for silicon dioxide layers to polysilicon layers and silicon nitride layers. 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 highly selective and low-foaming etching solution, characterized in that: The etching solution comprises 1-15 wt % of hydrofluoric acid, 10-25 wt % of ammonium fluoride, 0.01-0.3 wt % of additives, 0.05-0.5 wt % of surfactants, and the remainder is ultrapure water. The additive is at least one selected from poly(4-vinylpyridine toluenesulfonate), sodium polyanisyl sulfonate, poly(4-styrenesulfonic acid), potassium polydivinyl sulfonate, and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid). The surfactant is any one selected from alkoxy polyethylene hydroxyethanol, N-ethyl perfluorooctane sulfonamide ethanol, and ethoxylated-C12-18-alcohol.

2. A highly selective and low-foaming etching solution 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. A highly selective and low-foaming etching solution according to claim 1, characterized in that: The ammonium fluoride in the etching solution is electronic grade, and the mass concentration is 38-41%.

4. A highly selective and low-foaming etching solution as claimed in claim 1, characterized in that: The resistivity of the ultrapure water at 25° C. is not less than 18 megohms.

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