Etching solution for removing polycrystalline silicon false gate

Abstract

The invention belongs to the field of integrated circuit electronic chemicals, and particularly relates to an etching solution for removing a polycrystalline silicon false gate, which mainly comprises quaternary ammonium hydroxide, alcohol, an organic solvent, an anisotropic etching weakening additive and water. The etching liquid is mainly used for removing polycrystalline silicon false gates in the semiconductor manufacturing process, and the liquid medicine has certain organic polymer cleaning capacity and can synchronize polymer residues formed after dry etching. After being treated by the liquid medicine, no polymer or polycrystalline silicon is left on the surface of the structure, and the liquid medicine has high stability and long service life.

Description

Technical Field

[0001] This invention belongs to the field of electronic chemicals, specifically relating to the preparation of an etching solution for removing false gates in polycrystalline silicon and its application method. Background Technology

[0002] In semiconductor manufacturing, dummy poly removal is a key step in advanced processes, particularly important in technology nodes such as FinFET / GAA, HKMG processes, and multi-patterning techniques. It primarily addresses issues of process uniformity and structural integrity. Dummy poly removal can resolve problems such as CMP non-uniformity and gate profile distortion. Currently, wet etching is the mainstream method. According to the IRDS 2022 roadmap, by 2025, the dummy poly removal process needs to control critical dimension deviations to <0.8nm, driving the transition from wet to dry / wet hybrid methods. In dry etching, commonly used fluorine-containing gases (such as CF4, CHF3, C4F8, etc.) react with silicon after plasma dissociation to form fluorine radicals (F*), generating volatile SiF4. However, carbon readily combines with unsaturated fluorides to form long-chain fluorocarbon polymers (such as CXFY), which deposit on the etched surface or sidewalls. In such cases, wet etching is used, requiring the wet etching solution to have a certain polymer removal capability. Polycrystalline silicon is composed of multiple single-crystal silicon grains, and etching silicon under alkaline conditions exhibits anisotropy. The (111) facet is etched much slower than other crystal faces. In processes below 14nm, due to the small CD, when using alkaline reagents to etch polycrystalline or monocrystalline silicon, the etching stops when the (111) facet is encountered. The stopping position is V-shaped, and the two sides of the V-shape are the (111) facets of Si. Alternatively, a small amount of silicon residue may remain at the bottom of the structure. This residue requires a large amount of over-etching to remove it. However, increasing the over-etching time has a great impact on other parts of the structure. Therefore, it is necessary to reduce the anisotropy of alkaline etching and completely remove the silicon residue. Summary of the Invention

[0003] In order to meet the requirements of the current integrated circuit industry's transformation from wet to dry / wet hybrid methods, this invention improves the shortcomings of the strong anisotropy of existing poly etching solutions and adds polymer cleaning function.

[0004] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: An etching solution for removing false gates in polycrystalline silicon, the main components of which include quaternary ammonium hydroxide, alcohol, organic solvent, an anisotropic etching additive, and water.

[0005] In the above scheme, the quaternary ammonium hydroxide contains an organic base with the general formula R4NOH, where R is an organic base with four identical or different aliphatic or aromatic groups. Etching silicon under alkaline conditions involves two steps: first, the hydrogen adsorbed on the silicon surface is replaced by hydroxyl groups, resulting in hydroxylation; this step polarizes the Si-Si bonds. Second, water, acting as a nucleophile, attacks the polarized Si-Si bonds three times, causing silicon atoms to detach from the surface and form orthosilicic acid. The quaternary ammonium hydroxide has excellent electrolytic properties, capable of ionizing a large number of hydroxide ions, making the solution strongly alkaline and accelerating the hydroxylation reaction of polycrystalline silicon. The quaternary ammonium hydroxide used is one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, trimethylethylammonium hydroxide, triethylmethylammonium hydroxide, dimethyldiethylammonium hydroxide, trimethylphenylammonium hydroxide, benzyltrimethylammonium hydroxide, hexadecyltrimethylammonium hydroxide, and 1-adamantyltrimethylammonium hydroxide, with a content of 1%-15%.

[0006] In the above scheme, the alcohol is a small molecule alcohol. Alcohol can enhance the wettability of the solution on the silicon surface and accelerate the hydroxylation step. The small molecule alcohol includes one or more of methanol, ethanol, propanol, isopropanol, propylene glycol, ethylene glycol, and glycerol, with a content of 5%-20%.

[0007] In the above scheme, the organic solvent can dissolve the etched polymer within it, and the polarity of the solution is more conducive to the polarization of Si-Si bonds, making it easier for nucleophiles to break Si-Si bonds. The organic solvent includes ethers such as anisole, diethylene glycol butyl ether, propylene glycol methyl ether, 1,4-dioxane, tetrahydrofuran, 2-methyltetrahydrofuran, phenethyl ether, diethyl ether, diphenyl ether, and dibenzyl ether; macromolecular alcohols such as lauryl alcohol, n-hexanol, cyclohexanol, decanol, diacetone alcohol, furfuryl alcohol, polyethylene glycol, glycerol, and trimethylolpropane; and ammonium alkoxides. Monoethanolamine, diethanolamine, triethanolamine, N-methylethanolamine, N-ethylethanolamine, triisopropanolamine, N,N-dimethylethanolamine, 4-amino-1-butanol, methoxypropylamine, N-aminoethylpiperazine; hydrocarbons, such as xylene, cyclohexane, toluene; ketones, acetone, butanone, N-methylpyrrolidone, methyl isobutyl ketone; esters, such as ethyl acetate, ethyl lactate, γ-butyrolactone, propylene carbonate; and other highly polar solvents, such as sulfolane, dimethyl sulfoxide, acetonitrile, formamide; one or more of these substances, in a content of 20-70%.

[0008] In the above scheme, the anisotropic etching additive is hexamethylenediamine and its derivatives. Experiments have shown that this type of additive accelerates the etching rate of the (111) facet of silicon under alkaline conditions. In processes below 14nm, due to the small CD, when commonly used alkaline reagents are used to etch polycrystalline or monocrystalline silicon, the etching stops when the (111) facet is encountered. The stopping position is V-shaped, and the two sides of the V-shape are the (111) facets of Si. After adding this type of additive, the etching of the (111) facet is accelerated, reducing the anisotropy of the etching, and the etching will not stop or leave residue. The anisotropic etching additive can be one or more of hexamethylenediamine, N-acetylhexamethylenediamine, N-dodecylhexamethylenediamine, N,N-dibenzylhexamethylenediamine, N,N-diacetylhexamethylenediamine, and hexamethylenediamine bisquaternary ammonium salt, with a content of 0.1-5%.

[0009] In the above scheme, the temperature of the medicinal solution is 25-80℃, and the preferred temperature is 50-70℃.

[0010] This invention effectively removes residual polymer from the surface after dry etching and reduces the selectivity of the (100) / (111) crystal plane, resulting in no silicon residue after etching and a relatively stable solution with minimal change in heating rate over a long period. A comparison of the morphology before and after etching is shown in the attached figure. Attached Figure Description

[0011] Figure 1 The image shows the morphology of the TMAH anisotropic etched structure sheet after etching in Comparative Example 2.

[0012] Figure 2 The image shows the morphology of the etched structure sheet after etching to remove the polysilicon false gate in Example 1.

[0013] Figure 3 The image shows the etched morphology of the TMAH solution in Comparative Example 1, where some polymer (filamentous) was not completely cleaned.

[0014] Figure 4 The image shows the morphology after etching in Example 1, after complete polymer cleaning. Detailed Implementation

[0015] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0016] Examples 1-3 (1) Preparation method: Calculate the mass of each raw material required for the preparation of the etching solution by mass percentage. First, weigh the corresponding mass of pure water and put it in a container. There is no clear order of addition during the process. After the addition is completed, mix evenly to obtain the etching solution for removing polysilicon false gates.

[0017] (2) Etching conditions: 65℃.

[0018] (3) The examples contain different additives that reduce anisotropic etching and contain solvents. All percentages in the examples represent the mass percentage of the pure substance.

[0019] Comparative Example 1 (1) Preparation method: Calculate the mass of each raw material required for the etching solution by mass percentage. First, weigh the corresponding mass of pure water and put it in a container. There is no clear order of addition during the process. After adding, mix evenly to obtain Comparative Example 1.

[0020] (2) Etching conditions: 65℃.

[0021] (3) The comparative examples do not contain anisotropic etching additives and contain solvents. All percentages in the examples represent the mass percentage of the pure substance. Comparative Example 2 (1) Preparation method: Calculate the mass of each raw material required for the etching solution by mass percentage. First, weigh the corresponding mass of pure water and put it in a container. There is no clear order of addition during the process. After adding, mix evenly to obtain comparative example 3-4.

[0022] (2) Etching conditions: 65℃.

[0023] (3) The comparative examples do not contain anisotropic etching additives and are single TMAH or ADM solutions. Comparative Example 2 is a 2.38% TMAH solution.

[0024]

[0025] The above results indicate that the addition of organic solvents can effectively remove polymer residues, and the additives that weaken anisotropic etching can reduce the selectivity ratio of (100) / (111).

[0026] Examples 4-7 (1) Preparation method: Calculate the mass of each raw material required for the preparation of the etching solution by mass percentage. First, weigh the corresponding mass of pure water and put it in a container. There is no clear order of addition during the process. After the addition is completed, mix evenly to obtain an etching solution for removing polysilicon false gates.

[0027] (2) The etching temperatures in the examples are different and solvents are present. All percentages in the examples represent mass percentages of pure substances.

[0028] Comparative Examples 3-4 (1) Preparation method: Calculate the mass of each raw material required for the etching solution by mass percentage. First, weigh the corresponding mass of pure water and put it in a container. There is no clear order of addition during the process. After adding, mix evenly to obtain Comparative Example 3.

[0029] (2) The comparison examples have different etching temperatures, both lower and higher. All percentages in the examples represent the mass percentage of the pure material.

[0030] (4) Comparative Example 3 has a higher etching temperature of 40°C.

[0031]

[0032] The above examples and comparative examples illustrate that increasing the temperature is beneficial for polymer removal, and that anisotropy tends to increase with increasing temperature.

Claims

1. An etching solution for removing polysilicon dummy gates, characterized by: The main components of the solution include quaternary ammonium hydroxide, alcohol, organic solvent, anisotropy-reducing etching additive, and water.

2. The etching solution for removing polysilicon dummy gate according to claim 1, wherein: The quaternary ammonium hydroxide includes an organic base with the general formula R4NOH, wherein R is four identical or different aliphatic or aromatic hydrocarbon groups; the quaternary ammonium hydroxide includes one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, trimethylethylammonium hydroxide, triethylmethylammonium hydroxide, dimethyldiethylammonium hydroxide, trimethylphenylammonium hydroxide, benzyltrimethylammonium hydroxide, cetyltrimethylammonium hydroxide, and 1-adamantyltrimethylammonium hydroxide, and has a content of 1% to 15%.

3. The etching solution for removing polysilicon dummy gate according to claim 1, wherein: The alcohol is a small-molecule alcohol, and includes one or more of methanol, ethanol, propanol, isopropanol, propylene glycol, ethylene glycol, and glycerol, and has a content of 5% to 20%.

4. The etching solution for removing polysilicon dummy gate according to claim 1, wherein: The organic solvent includes any one or a combination of ketones, ethers, macromolecular alcohols, and alcohol amines.

5. The etching solution for removing polysilicon dummy gate according to claim 4, wherein: The ketones include acetone, butanone, N-methylpyrrolidone, and methyl isobutyl ketone; esters such as ethyl acetate, ethyl lactate, gamma-butyrolactone, and propylene carbonate.

6. The etching solution for removing polysilicon dummy gate according to claim 4, wherein: The ethers include anisole, diethylene glycol butyl ether, propylene glycol methyl ether, 1,4-dioxane, tetrahydrofuran, 2-methyltetrahydrofuran, phenyl ethyl ether, diethyl ether, diphenyl ether, and dibenzyl ether.

7. The etching solution for removing polysilicon dummy gate according to claim 4, wherein: The macromolecular alcohols include lauryl alcohol, n-hexanol, cyclohexanol, decanol, diacetone alcohol, furfuryl alcohol, polyethylene glycol, glycerol, and trihydroxymethyl propane.

8. The etching solution for removing polysilicon dummy gate according to claim 4, wherein: The alcohol amines include monoethanolamine, diethanolamine, triethanolamine, N-methylethanolamine, N-ethylethanolamine, triisopropanolamine, N,N-dimethylethanolamine, 4-amino-1-butanol, methoxypropylamine, and N-aminoethylpiperazine.

9. The etching solution for removing polysilicon dummy gate according to claim 1, wherein: The anisotropy-reducing etching additive is hexanediamine and its derivatives, and includes one or more of N-acetylhexanediamine, N-dodecylhexanediamine, N,N-dibenzylhexanediamine, N,N-diacetylhexanediamine, and hexanediamine bisquaternary ammonium salt, and has a content of 0.1% to 5%.

10. The etching solution for removing polysilicon dummy gate according to any one of claims 1-9, wherein: The etching temperature is 25-80°C, and the preferred temperature is 50-70°C. The polymer remaining on the dry surface after etching is removed, and the (100) / (111) selection ratio is reduced.

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