Deep trench polysilicon etching solution

Abstract

The application discloses a deep-groove polysilicon etching solution, which comprises an oxidizing agent, an inorganic acid, a pH regulator and a surfactant. The deep-groove polysilicon etching solution can efficiently etch polysilicon while ensuring the uniformity and smoothness of the etching surface, and can maximize the consistency of the etching of the upper and lower grooves and the smoothness of the surface. In the etching process, the inorganic acid ensures that the etching solution system is in an acidic environment, and the polysilicon is etched; the pH regulator avoids the large fluctuation of the pH of the etching solution, thereby ensuring the stability of the polysilicon etching process; and the surfactant reduces the surface tension of the etching solution, improves the wettability of the etching solution, ensures the consistency of the etching rate of the upper and lower grooves, and ensures the consistency of the groove aperture.

Description

Technical Field

[0001] This invention relates to the field of polycrystalline silicon technology, and more specifically to a deep trench polycrystalline silicon etching solution. Background Technology The 3D NAND technology published in recent years, which promotes the large capacity of memory by adopting three-dimensional structures, requires an etching solution that can precisely fabricate the desired three-dimensional structure.

[0002] The oxide layer on the surface of polysilicon reduces the etching rate or surface uniformity. Currently, acidic polysilicon etchants primarily use fluorinated compounds. In systems containing oxidants, these fluorinated compounds promote the etching of the substrate and silicon oxide, reducing the uniformity of polysilicon etching. As the size of microelectronic devices decreases, achieving the critical dimensions for vias and trenches becomes more difficult. If the etching process is performed at a high etching rate, a portion of the wafer has already been etched down to the gate oxide layer. However, in areas with low etching rates, thin layers of polysilicon remain to be etched away. Therefore, the use of an etchant capable of precisely etching vias and trenches is extremely urgent. Summary of the Invention

[0003] In view of the above, the present invention provides an etching solution capable of uniformly etching deep trench polysilicon structures.

[0004] This invention provides an etching solution for uniform etching of deep trench polysilicon, which uniformly etches the upper and lower structures of the deep trench while ensuring the polysilicon etching rate, ensuring that the surface of the deep trench and the bottom hole size are consistent, and at the same time, the surface roughness is low.

[0005] The deep trench structure is shown in the attached figure. Figure 1 As shown.

[0006] A deep trench polysilicon etching solution, the etching solution comprising the following raw materials by mass fraction: 5-20% inorganic acids; 1-10% oxidant; 0.1-5% pH adjuster; 0.01~2% surfactant; The remainder is deionized water.

[0007] Preferably, in the etching solution of the present invention, the oxidant includes one or a combination of several of hydrogen peroxide, nitric acid, perchloric acid, periodic acid, and ammonium persulfate.

[0008] The oxidant oxidizes polycrystalline silicon into silicon oxide. Under acidic conditions, hydrated hydrogen ions dissolve the silicon oxide, and the polycrystalline silicon is then etched.

[0009] Preferably, in the etching solution of the present invention, the inorganic acid is phosphoric acid, which ensures that the etching solution provides hydrogen ions to cooperate with the oxidant.

[0010] Preferably, in the etching solution of the present invention, the pH adjuster includes ammonium phosphate, ammonium acetate, diammonium hydrogen phosphate, citric acid, etc., which provide hydroxide ions through ionization and hydrolysis to ensure the acid-base balance of the etching solution, keep the pH of the etching solution in a stable state, and at the same time ensure that the etching solution system is an acidic environment with the pH maintained at 1-6.

[0011] More preferably, the pH of the etching solution system of the present invention is maintained at 1-2.

[0012] Preferably, in the etching solution of the present invention, the surfactant includes dodecylbenzenesulfonic acid, heptanoic acid, L-44, octanoic acid, octylamine, polyethylene glycol, ethylene glycol, and glycerol, which improves the physical properties of the etching solution, such as surface tension, contact angle, and wettability, so that the etching solution can better contact the polycrystalline silicon, ensure that the etching rate is consistent above and below the polycrystalline silicon via, and ensure the uniformity of the via structure.

[0013] The advantages of this invention are: (1) The etching solution of the present invention contains phosphoric acid, which is mild and stable, and can release hydrogen ions in stages. The system is stable, ensuring uniform etching of polysilicon on the trench surface and avoiding surface roughness caused by violent system reaction, which has certain defects.

[0014] (2) In the etching solution of the present invention, the pH adjusters ammonium phosphate, ammonium acetate, diammonium hydrogen phosphate, citric acid, etc. provide hydroxide ions through ionization and hydrolysis to ensure the acid-base balance of the etching solution, keep the pH of the etching solution in a stable state, and at the same time ensure that the etching solution system is an acidic environment to ensure a stable etching rate of polycrystalline silicon.

[0015] (3) In the etching solution of the present invention, the surfactants dodecylbenzenesulfonic acid, heptanoic acid, L-44, octanoic acid, octylamine, polyethylene glycol, glycerol, etc., prevent the formation of etching residues and improve the physical properties of the etching solution, such as surface tension, contact angle, wettability, etc., so that the etching solution can better contact the metal copper and ensure the etching rate of the metal copper.

[0016] (4) The etching solution of the present invention does not contain fluorine-containing compounds, so as to avoid etching the silicon substrate in a system containing oxidants.

[0017] This invention provides an etching solution that uniformly etches the upper and lower structures of a deep trench, ensuring that the surface of the deep trench and the bottom hole diameter are consistent, while having a low surface roughness. Attached Figure Description

[0018] Figure 1It is a polycrystalline silicon trench structure, through which the etching solution enters to etch the polycrystalline silicon. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] The etching solution, prepared according to the proportions in the table, was used to perform an immersion etching experiment on a deep trench polycrystalline silicon wafer at 30°C for 60 minutes. To avoid contamination of the polycrystalline silicon structure, it was first spray-cleaned with electronic-grade IPA and the surface was dried with nitrogen to ensure a clean surface. After slicing, the aperture size was measured by SEM scanning of the cross-section and recorded as the initial aperture S1. After etching, the wafer was cleaned with deionized water, and the aperture size of the upper, middle, and lower sections of the deep trench was measured by SEM scanning of the cross-section and recorded as the aperture size after etching S2. The aperture size and etching rate were calculated by the changes in aperture size before and after etching.

[0021] The calculation formula is as follows: u = (S2 - S1) / t, Where u is the etching rate, which is the thickness of polysilicon etched by the etchant per unit time, in Å / min; S1 is the aperture before etching, in Å; S2 is the aperture after etching, in Å; t represents the etching time, in minutes.

[0022] Table 1 shows the components and contents of the examples and comparative examples.

[0023] Table 2 shows the etching rates at the top, middle, and bottom positions of the deep trench polysilicon structure.

[0024] Table 3 shows the surface roughness of deep trench polysilicon structures.

[0025] The evaluation results in Table 2 show that the etching solution composition of the examples improves the surface tension of the etching solution system by adding surfactants, enhances the wettability of the etching solution in the trench system, ensures full contact between the etching solution and the surface to be etched, and shows that the etching rate of the upper, middle and lower polysilicon layers of the trench structure is not significantly different, and the etching rate of the upper and lower layers remains basically consistent.

[0026] In Comparative Examples 1-7, Comparative Example 1 did not contain a surfactant, so the surface tension of the etching solution was high and the difference between the upper and lower layers was the greatest. Comparative Examples 2-3 did not contain a pH adjuster, so the etching rate was relatively slow due to pH fluctuations in the system. In Comparative Examples 4-7, different amounts of surfactant were selected for comparison. Under the conditions of two different surfactant combinations, when the content was 0.5% / 1%, the etching rate of the upper and lower layers could be basically guaranteed to be consistent.

[0027] The surfactant described in this invention is used to reduce the surface tension of the etching solution, improve wettability, and reduce the difference in etching rates of the upper, middle, and lower polysilicon layers in the deep trench structure.

[0028] The etching solution can reduce the difference in etching rate between the upper, middle and lower polysilicon layers of the concave trench structure, and keep the etching rate of the upper, middle and lower layers basically the same.

[0029] Data from Example 7 shows that the addition of a fluorine-containing compound increases the polysilicon etching rate. However, the presence of an oxidant in the system leads to surface delamination. This invention provides a polysilicon etching solution capable of stably etching deep trench structures, free of fluorides, ensuring uniform trench etching while maintaining a smooth surface.

[0030] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The embodiments and features described in these embodiments can be arbitrarily combined without conflict. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A deep trench polysilicon etching solution, characterized by, The etching solution comprises the following raw materials by mass fraction: 5-20% of inorganic acid; 1-10% of oxidizing agent; 0.1-5% of pH regulator; 0.01-2% of surfactant; the balance being deionized water; the oxidizing agent comprises one or a combination of hydrogen peroxide, nitric acid, perchloric acid, periodic acid, and ammonium persulfate; the inorganic acid is phosphoric acid; the pH regulator comprises one or a combination of ammonium phosphate, ammonium acetate, disodium hydrogen phosphate, and citric acid; the surfactant comprises one or a combination of dodecyl benzene sulfonic acid, heptanoic acid, L-44, octanoic acid, octylamine, polyethylene glycol, ethylene glycol, and glycerol.

2. The deep trench polysilicon etching solution of claim 1, wherein The pH range of the etching solution is 1-6.

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