An etching solution for etching silicon dioxide with high selectivity relative to doped polysilicon

Abstract

The present invention provides an etching solution for etching silicon dioxide with high selectivity relative to doped polysilicon, for example, boron-doped polysilicon and boron-phosphorus-doped polysilicon, and the etching solution comprises hydrofluoric acid, ammonium fluoride, additives, organic acids and ultrapure water. The etching solution of the present invention can obtain an etching solution with low surface tension and excellent wettability through the action of the additives, and the addition of the additives and organic acids has a protective effect on the doped polysilicon, and can form a stable protective film on the surface of the doped polysilicon, selectively etching silicon dioxide, and the etching selectivity ratio of silicon dioxide to doped polysilicon can reach more than 2000, and the surface roughness of the doped polysilicon layer after etching is less than 0.050nm. The etching solution of the present invention has a better protective effect on the doped polysilicon layer without affecting the etching rate of the silicon dioxide layer and the silicon nitride film layer.

Description

Technical Field

[0001] The invention belongs to the field of etching liquid, in particular to an etching liquid capable of etching silicon dioxide with high selectivity relative to doped polysilicon. Background Art

[0002] In the manufacture of integrated circuits and other electronic devices, multiple layers of conductive materials, semiconductor materials, and dielectric materials are deposited on the surface of a semiconductor wafer, or these layers of materials are removed from the surface of a semiconductor wafer. A method for isolating the components of a semiconductor device is called a shallow trench isolation (STI) process, which generally includes using a silicon nitride layer formed on a silicon substrate, forming a shallow trench in the silicon nitride layer, and depositing a dielectric material (e.g., oxide) to fill the trench. Excess dielectric material is usually deposited on top of the substrate to ensure that the trench is completely filled.

[0003] At present, in the manufacture of integrated circuits, it is required to etch as little polysilicon as possible while etching silicon dioxide and silicon nitride, stably protect the polysilicon layer, and at the same time, the silicon dioxide layer and the silicon nitride layer have a certain etching selectivity. Generally, a buffered oxide etchant (HF+NH4F+DIW) is used to etch and remove the silicon dioxide layer and the silicon nitride layer, but conventional buffered oxide etchants will result in a low etching selectivity of silicon dioxide and silicon nitride, and will cause more loss of the polysilicon layer, which is not conducive to selective controllable etching. With the development of chip manufacturing process, the aspect ratio has developed from 5-10:1 to more than 80:1, and the number of storage layers has also developed from 32 layers to 232 layers. Conventional buffered oxide etching solutions have high surface tension and poor wettability, and cannot quickly wet into the deep hole structure of silicon oxide and silicon nitride stacks. The upper, middle and lower layers of the deep hole structure are etched inconsistently due to different contact time with the etching solution, resulting in residual silicon dioxide in the middle and lower layers of the structure. In addition, due to the high surface tension of the etching solution, the surface roughness of polysilicon after etching will also be high. Summary of the invention

[0004] The present invention provides an etching solution for etching silicon dioxide with high selectivity relative to doped polysilicon, which can quickly wet into a deep hole structure and completely etch the silicon dioxide layer in the deep hole structure, while protecting the doped polysilicon layer from being etched in small amounts without affecting the etching rates of the silicon dioxide layer and the silicon nitride layer.

[0005] The technical solution of the present invention is an etching solution for etching silicon dioxide with high selectivity relative to doped polysilicon, wherein the etching solution comprises 2-8wt% hydrofluoric acid, 10-25wt% ammonium fluoride, 0.01-0.1wt% additives, 0.01-0.1wt% organic acid, and the remainder is ultrapure water.

[0006] Furthermore, the additive is a carboxyl-containing anionic surfactant, including one or more of dodecyl succinic acid, polyepoxysuccinic acid, fatty alcohol polyoxyethylene ether carboxylic acid, and isomeric decanol polyoxyethylene ether carboxylic acid. The above additives have excellent solubility in the etching solution and will not precipitate. They have an inhibitory effect on the etching rate of the doped polysilicon layer and the silicon nitride layer. However, the carboxyl-containing anionic surfactant cannot be a carboxylic acid metal salt type, as the carboxylic acid metal salt type will introduce metal impurities into the etching solution.

[0007] Furthermore, the organic acid is one or more of acetic acid, oxalic acid, citric acid, lactic acid, succinic acid, malic acid, and ascorbic acid.

[0008] Furthermore, the doped polysilicon includes boron-doped polysilicon and boron-phosphorus-doped polysilicon.

[0009] Furthermore, the pH value of the highly selective etching solution is 5-6. The pH value of the etching solution will affect the etching rate. The lower the pH value, the stronger the acidity, the faster the etching rate of silicon oxide and silicon nitride, which is not conducive to the precise control of etching; the higher the pH value, the weaker the acidity, the slower the etching rate of silicon oxide and silicon nitride, the selectivity for doped polysilicon decreases, the etching time is prolonged, and the processing efficiency is reduced.

[0010] Furthermore, the highly selective etching is the selective etching of the etching solution on the silicon dioxide layer and the doped polysilicon layer, and the selectivity ratio can reach more than 2000.

[0011] Furthermore, the highly selective etching solution does not affect the etching rates of the silicon dioxide layer and the silicon nitride layer, the selectivity ratio of the silicon dioxide layer and the silicon nitride layer is maintained at about 22, and the surface roughness of the doped polysilicon layer after etching is below 0.050 nm.

[0012] The present invention has the following beneficial effects:

[0013] 1. In the present invention, the addition of additives can obtain an etching solution with low surface tension and excellent wettability, which can quickly wet into the laminated deep hole structure of silicon oxide and silicon nitride and completely etch the silicon dioxide layer in the deep hole structure; since the polycrystalline silicon layer is doped with boron, the trivalent boron doped into the tetravalent silicon will generate "holes" in the crystal structure, which can easily attract electrons to combine, and the carboxyl-containing anionic surfactant is negatively charged after dissociation, which can combine with the holes in the boron-doped polycrystalline silicon and adsorb on the surface of the doped polycrystalline silicon to form a protective film. The pH of the etching solution is controlled at 5-6, which can ensure the etching effect and efficiency while also having an excellent protective effect on the doped polycrystalline silicon.

[0014] 2. Under the premise of not affecting the etching rates of the silicon dioxide layer and the silicon nitride layer, the etching solution of the present invention maintains a selectivity ratio of the silicon dioxide layer and the silicon nitride layer at about 22, and a selectivity ratio of the silicon dioxide layer and the doped polysilicon layer can reach more than 2000, and the surface roughness of the doped polysilicon layer after etching is below 0.050 nm. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the structure of each membrane layer in the deep hole stacked structure.

[0016] Figure 2 It is a schematic diagram of the structure after etching with the etching solution of the present invention. The etching solution of the present invention has low surface tension and excellent wettability, and the upper, middle and lower layers of the laminated structure have excellent etching uniformity after etching.

[0017] Figure 3 This is a schematic diagram of the structure after etching with an etching solution without additives. Since there is no additive, the surface tension is high and the wettability is poor. After etching the stacked structure, the etching uniformity of the upper, middle and lower layers is poor. DETAILED DESCRIPTION

[0018] The embodiments of the present invention will be described in detail below with reference to examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention.

[0019] In order to verify the etching selectivity effect of the etching solution, thermal silicon dioxide single-layer wafer, CVD silicon nitride single-layer wafer, and boron-phosphorus doped polysilicon single-layer wafer were used. The etching rate was calculated by measuring the thickness before and after etching with an ellipsometer, and AFM was used to detect the roughness of the boron-phosphorus doped polysilicon layer after etching.

[0020] The etching temperature used in the embodiment of the present invention is 23° C., the silicon dioxide etching time is 1 min, the silicon nitride etching time is 3 min, the boron-phosphorus doped polysilicon etching time is 30 min, and the etching method is stirring etching.

[0021] The components and contents in the examples are shown in Table 1.

[0022] Table 1

[0023]

[0024]

[0025] The experimental results are shown in Table 2.

[0026] Table 2

[0027]

[0028]

[0029] It can be seen from Table 2 that the etching selectivity ratios of the silicon dioxide layer and the boron-phosphorus doped polysilicon layer in Examples 1-7 are all greater than 2000, and the etching rate difference between the silicon dioxide layer and the silicon nitride layer is not obvious. The etching selectivity ratios of the silicon dioxide layer and the silicon nitride layer are both 22-23, and the roughness of the boron-phosphorus doped polysilicon layer after etching is less than 0.020nm.

[0030] Comparative Example 1 does not contain additives and organic acids, the etching rates of the silicon nitride layer and the boron-phosphorus doped polysilicon layer are fast, the roughness after etching is large, and the etching selectivity of the silicon dioxide and boron-phosphorus doped polysilicon layers can only reach about 270. Comparative Example 2 contains only additives, the etching rates of the silicon dioxide layer and the silicon nitride layer are consistent with those in the embodiment, and there is only a certain protective effect on the boron-phosphorus doped polysilicon layer, and the selectivity is only increased to 944. Comparative Example 3 contains only organic acids. Although there is a certain protective effect on the boron-phosphorus doped polysilicon layer, the etching rate of the silicon nitride layer is too fast, the etching selectivity of the silicon dioxide layer and the silicon nitride layer is only 7.78, and the roughness of the boron-phosphorus doped polysilicon layer after etching is large. Comparative Example 4 contains additives and organic acids, the additive content is less than 0.01wt%, the etching rate of the silicon nitride layer is higher than that of the embodiment, the etching selectivity of the silicon dioxide layer and the silicon nitride layer does not reach 22, the protective effect on the boron-phosphorus doped polysilicon layer is weaker than that of the embodiment, and the roughness of the boron-phosphorus doped polysilicon layer after etching is also high. Comparative Example 5 contains additives and organic acids, and the content of the additives is higher than 0.1 wt%. The etching selectivity of the silicon dioxide layer and the boron-phosphorus doped polysilicon layer is not significantly improved, and too high an additive content will also introduce more metal impurities into the etching solution, which will affect the quality of the product. Comparative Example 6 contains additives and organic acids, and the content of the organic acid is lower than 0.01 wt%. The protective effect on the boron-phosphorus doped polysilicon layer is weaker than that in the embodiment. Comparative Example 7 contains additives and organic acids, and the content of the organic acid is higher than 0.1 wt%. Although it has an excellent protective effect on the boron-phosphorus doped polysilicon layer, the etching rate of the silicon nitride layer is significantly improved, and the etching selectivity of the silicon dioxide layer and the silicon nitride layer is only about 13.

[0031] In comparative example 8, the additive is dodecylbenzene sulfonic acid, and the sulfonic acid surfactant can significantly increase the etching rate of the silicon nitride layer, but the protective effect on the boron-phosphorus doped polysilicon layer is weaker than that of the embodiment of the present invention. In embodiment 9, the additive is fatty alcohol polyoxyethylene ether phosphate, and although it has an excellent protective effect on the boron-phosphorus doped polysilicon layer, the phosphate surfactant can significantly reduce the etching rate of the silicon dioxide layer and increase the etching rate of the silicon nitride layer. In comparative examples 10 and 11, the additives are nitrogen-containing heterocyclic carboxylic acids and oxygen-containing heterocyclic carboxylic acids, and although they have a protective effect on the boron-phosphorus doped polysilicon layer, they have no obvious inhibitory effect on the etching rate of silicon nitride, and the etching selectivity of the silicon dioxide layer and the silicon nitride layer is only about 10, and the heterocyclic additives are easy to precipitate, resulting in a large roughness of the boron-phosphorus doped polysilicon layer.

[0032] In Comparative Example 12, the hydrofluoric acid content is increased, and the pH of the etching solution is reduced. When the pH is below 5, although the etching selectivity of the silicon dioxide layer and the boron-phosphorus doped polysilicon layer can reach 7000, the etching rate of the silicon dioxide layer is too fast. Under the premise of etching the silicon dioxide layer of the same thickness, the etching time is 30s in the embodiment, and only 7s is required in Comparative Example 12. Too short an etching time will lead to a large etching deviation, which is not easy to accurately control. In Comparative Example 13, the pH of the etching solution is higher than 6, and the etching rates of the silicon dioxide layer, the silicon nitride layer, and the boron-phosphorus doped polysilicon layer are all reduced. The etching selectivity of the silicon dioxide layer and the silicon nitride layer is only about 18, and the etching selectivity of the silicon dioxide layer and the boron-phosphorus doped polysilicon layer is only 633. In addition, the etching rate is reduced, the etching time needs to be extended, and the processing efficiency is reduced.

[0033] Obviously, the above embodiments and comparative examples are only examples for clearly explaining the invention, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description, and it is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

[0034] The above-mentioned embodiments are only preferred technical solutions of the present invention and should not be regarded as limitations of the present invention. The embodiments and features in the embodiments of the present application can be arbitrarily combined with each other without conflict. The protection scope of the present invention shall be the technical solutions recorded in the claims, including the equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. An etching solution for etching silicon dioxide with high selectivity relative to doped polysilicon, characterized in that: The etching solution comprises 2-8 wt% of hydrofluoric acid, 10-25 wt% of ammonium fluoride, 0.01-0.1 wt% of additives, 0.01-0.1 wt% of organic acid, and the balance is ultrapure water; the additive is one of dodecyl succinic acid, polyepoxy succinic acid, and fatty alcohol polyoxyethylene ether carboxylic acid; the doped polysilicon comprises boron-doped polysilicon or boron-phosphorus-doped polysilicon, and the pH of the etching solution is 5-6; the organic acid is one or more of acetic acid, oxalic acid, citric acid, lactic acid, succinic acid, malic acid, and ascorbic acid.

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