A highly selective and low-corrosive silicon nitride etching solution, its preparation method and application

Abstract

The present invention relates to a highly selective and low-corrosion silicon nitride etching solution, its preparation method and application. The etching solution comprises: a product obtained by reacting 2-5 parts of 1-vinylsilatrane and 0.8-10 parts of pyrophosphoric acid, 75-90 parts of concentrated phosphoric acid and 12-16 parts of ultrapure water. Among them, pyrophosphoric acid reacts with 1-vinylsilatrane to generate a product that has the functions of inhibiting the corrosion of SiO2, protecting polysilicon, improving the etching selectivity of Si3N4 / SiO2 and Si3N4 / polysilicon, helping to decompose etching by-products, accelerating the Si3N4 etching reaction, and increasing the solubility in concentrated phosphoric acid, and can be applied in the field of silicon nitride etching of 3D flash memory chips.

Description

Technical Field

[0001] The present invention belongs to the field of etching solutions, and particularly relates to a silicon nitride etching solution with high selectivity and low corrosion, and a preparation method and application thereof. Background Art

[0002] In the manufacturing process of 3D NAND flash memories, silicon nitride (Si 3 N 4 ) and silicon oxide (SiO 2 ) are usually deposited in multiple layers alternately. After that, dry etching and polysilicon deposition are carried out. Finally, the silicon nitride layer is etched laterally completely by high-temperature phosphoric acid (H 3 PO 4 ), and then depositions of various storage layers and isolation layers are carried out.

[0003] When the silicon nitride layer is etched laterally in high-temperature H 3 PO 4 , not only the silicon oxide layer will be etched, resulting in the thinning of the silicon oxide layer, but also, as the silicon nitride layer is continuously etched laterally, the deposited polysilicon layer will be exposed in the later stage of etching. When the polysilicon is placed in a phosphoric acid environment, it will also be corroded. And because the etching solution needs to be maintained at a high temperature (above 150°C / 160°C) for dozens or even hundreds of hours, the existing etching solutions usually add organic additives to phosphoric acid. As the etching time prolongs, with the progress of etching, the silicon content in the etching solution increases, resulting in a decrease in the etching rate of silicon nitride.

[0004] Therefore, it is necessary to develop a silicon nitride etching solution with high selectivity and low corrosion that can simultaneously improve the etching selectivity ratio of Si 3 N 4 / SiO 2 and the etching selectivity ratio of Si 3 N 4 / polysilicon. Summary of the Invention

[0005] The technical problems solved by the present invention are that the silicon nitride etching solution is prone to corrosion during the etching process and has a relatively low etching selectivity ratio for Si3N4 / SiO2 and Si3N4 / polysilicon.

[0006] In view of the technical problems existing in the prior art, the present invention designs a silicon nitride etching solution with high selectivity and low corrosion, a preparation method and an application thereof.

[0007] It should be noted that in the present invention, unless otherwise specified, the specific meaning of "including" involving composition limitations and descriptions includes both the open "including", "containing" and their similar meanings, and also includes the closed "consisting of..." and their similar meanings.

[0008] To solve the above-mentioned existing technical problems, the present invention adopts the following solutions:

[0009] [First technical solution]

[0010] In the first aspect, a technical solution of the present invention lies in providing a silicon nitride etching solution with high selectivity and low corrosion. Calculated by weight parts, the etching solution contains: a product obtained by reacting 2-5 parts of 1-vinylsilatrane and 0.8-10 parts of pyrophosphoric acid, 75-90 parts of concentrated phosphoric acid, and 12-16 parts of ultrapure water.

[0011] Furthermore, the mass ratio of the 1-vinylsilatrane to the pyrophosphoric acid is preferably (3-5):(3.5-4.5).

[0012] Furthermore, the mass ratio of the 1-vinylsilatrane to the pyrophosphoric acid is more preferably 4:3.6.

[0013] Furthermore, the mass parts of the concentrated phosphoric acid are preferably 80-85 parts.

[0014] Furthermore, the mass parts of the ultrapure water are preferably 13-15 parts.

[0015] Furthermore, the ultrapure water is deionized water with a resistance ≥ 18 MΩ.

[0016] Furthermore, the reaction product of the 1-vinylsilatrane and the pyrophosphoric acid includes a phosphosilicate ester shown in Formula 1 and triethanolamine phosphate.

[0017] [Second technical solution]

[0018] In the second aspect, a technical solution of the present invention lies in providing a preparation method of the above-mentioned silicon nitride etching solution. The specific preparation method is as follows:

[0019] Step 1: Stir and mix pyrophosphoric acid and 1-vinylsilatrane at 70-90 °C for 2 h for reaction;

[0020] Step 2: After the above reaction is completed, cool to room temperature, add concentrated phosphoric acid and ultrapure water to the solution in Step 1, and continue to stir and mix to obtain the silicon nitride etching solution.

[0021] In Step 1, the 1-vinylsilatrane and the pyrophosphoric acid react as follows:

[0022] .

[0023] It can be seen from the above reaction that the 1-vinylsilatrane and the pyrophosphoric acid obtain two reaction products, namely a phosphosilicate ester shown in Formula 1 and triethanolamine phosphate. The two reaction products have multiple important functions, which are specifically as follows:

[0024] First, the phosphosilicate ester described in Formula 1 has multiple Si-OH bonds, making it easy to adsorb on the SiO2 layer and form a protective film on the SiO2 surface through van der Waals forces, inhibiting the further etching of SiO2 by the etching solution and improving the Si3N4 / SiO2 etching selectivity.

[0025] Second, 1-vinyltriazasilane has an ethylene group. The phosphosilicate ester formed by reacting with pyrophosphoric acid still retains the ethylene group. The ethylene group can be protonated, making itself positively charged. Since the polysilicon surface has electronegativity, the two can undergo electrostatic interaction, thereby protecting the polysilicon surface and improving the Si3N4 / polysilicon selectivity, ensuring that the polysilicon is not affected by the etching solution when exposed to the etching solution.

[0026] Third, in addition to the main product phosphosilicate ester, a certain amount of triethanolamine phosphate exists in the etching solution, which can help decompose the etching by-products and further accelerate the Si3N4 etching reaction kinetically.

[0027] Fourth, the phosphate group in the phosphosilicate ester described in Formula 1 can increase its solubility in concentrated phosphoric acid, effectively solving the problem that existing silicon-based compounds are not easily soluble in concentrated phosphoric acid.

[0028] In summary, the two products formed by the reaction of pyrophosphoric acid and 1-vinyltriazasilane in the etching solution components both play roles in the etching solution, which is of great significance.

[0029] [The third technical solution]

[0030] In a third aspect, a technical solution of the present invention lies in providing the use of the silicon nitride etching solution for etching the silicon nitride layer in a storage NAND chip.

[0031] [The fourth technical solution]

[0032] In a fourth aspect, a technical solution of the present invention lies in providing an etching method for the silicon nitride etching solution, including the following steps:

[0033] Step 1: Immerse the silicon nitride sample wafer in an etching device filled with the silicon nitride etching solution at 157°C - 160°C, and the immersion time is determined according to the thickness to be etched;

[0034] Step 2: Rinse the immersed silicon nitride sample wafer in ultrapure water at least twice, that is, complete the rinsing step of the silicon nitride wafer;

[0035] Step 3: Quickly dry the surface with a nitrogen gun.

[0036] Further, the etching device in Step 1 is sealed to prevent the evaporation of ultrapure water.

[0037] The present invention provides a silicon nitride etching solution with high selectivity and low corrosion, a preparation method thereof, and an application thereof, which have the following beneficial effects:

[0038] 1. In the present invention, 1-vinylsilatrane and pyrophosphoric acid are reacted to obtain a main product, phosphosilicate, which has multiple Si-OH bonds and vinyl groups. The Si-OH bonds enable it to easily adsorb on the SiO2 layer and form a protective film on the SiO2 surface through van der Waals forces, inhibiting the further etching of SiO2 by the etching solution; the vinyl groups can be protonated to make themselves positively charged, and can have electrostatic interaction with the polysilicon surface, realizing the protection of the SiO2 layer and polysilicon by physical and chemical actions, and improving the selectivity of Si3N4 / polysilicon and Si3N4 / SiO2.

[0039] 2. In the present invention, 1-vinylsilatrane and pyrophosphoric acid are reacted to obtain a by-product, triethanolamine phosphate, which can help decompose the etching by-products, and thus accelerate the Si3N4 etching reaction.

[0040] Therefore, the silicon nitride etching solution of the present invention has very good application prospects and the potential for large-scale industrial promotion in the field of silicon nitride etching solutions for 3D flash memory chips. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 : Infrared spectrum diagram of the phosphosilicate prepared in Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0042] The present invention will be further described below with reference to specific examples and the accompanying drawings:

[0043] Preparation methods of silicon nitride etching solutions of Examples 1-5 and Comparative Examples 1-2 of the present invention:

[0044] Step 1: Stir and mix pyrophosphoric acid and 1-vinylsilatrane at 80 °C for 2 h;

[0045] Step 2: After the above reaction is completed, cool to room temperature, add concentrated phosphoric acid and ultrapure water to the solution in Step 1, and continue to stir and mix to obtain the silicon nitride etching solution.

[0046] Table 1: Silicon nitride etching solutions of Examples 1-5

[0047]

[0048] Table 2: Silicon nitride etching solutions of Comparative Examples 1-2

[0049]

[0050] Preparation method of silicon nitride etching solution of Comparative Example 3:

[0051] At room temperature, 7.6 parts by weight of triethanolamine phosphate (CAS No.: 10017-56-8), 80 parts of concentrated phosphoric acid and 14 parts of ultrapure water were stirred and mixed evenly to obtain the silicon nitride etching solution Comparative Example 3.

[0052] Table 3: Test data of Examples 1-5 and Comparative Examples 1-3

[0053]

[0054] The etching method using the above etching solution for 3D flash memory chips is as follows:

[0055] Step 1: Introduce the silicon nitride etching solution into the etching tank, and soak the silicon nitride sample wafer at 160 °C using the above etching solution. The etching device is sealed to prevent water evaporation, and the soaking time is determined according to the thickness to be etched.

[0056] Step 2: Put the soaked silicon nitride sample wafer into ultrapure water and rinse it at least twice to complete the rinsing step of the silicon nitride wafer.

[0057] Step 3: Quickly dry the surface with a nitrogen gun.

[0058] Regarding performance testing and description:

[0059] The test method for Performance 1 etching rate is as follows:

[0060] Introduce the silicon nitride etching solution into the etching tank, and then soak the silicon nitride wafer, silicon dioxide wafer and polysilicon wafer at 160 °C using the etching solution. The thickness of the silicon nitride wafer and the silicon dioxide wafer is 3000 Å, and the thickness of the polysilicon wafer is 1600 Å. The silicon dioxide wafer and the polysilicon wafer are each soaked for 60 minutes. The film thickness before and after etching is measured by a film thickness meter and the etching rate is calculated. The etching rate of the silicon nitride wafer is calculated according to its complete etching time. When the silicon nitride is completely etched, the silicon surface will be exposed. The silicon surface is hydrophobic and has a gray bright surface, which is different from the color of the silicon nitride (pink). Whether the silicon nitride is completely etched is judged by the color change.

[0061] Put the etched silicon nitride wafer, silicon dioxide wafer and polysilicon wafer into ultrapure water and rinse them at least twice, and then quickly dry the surface with a nitrogen gun to complete the treatment to obtain the etched silicon nitride wafer, silicon oxide wafer and polysilicon wafer; the film thickness before and after etching is measured by a film thickness meter and the etching rate is calculated.

[0062] The ultrapure water used in the above steps is deionized water with a resistance of at least 18 MΩ.

[0063] Regarding the analysis and description of the test results:

[0064] As can be seen from Table 3, compared with the comparative examples, the etching solution of the embodiment of the present invention significantly increases the etching rate of silicon nitride and reduces the etching rates of silicon dioxide and polysilicon.

[0065] In the etching solution of Comparative Example 1, only pyrophosphoric acid is added, which cannot protect the SiO 2 layer / polysilicon layer, resulting in an increase in the etching rates of silicon dioxide and polysilicon and a decrease in the selectivity.

[0066] When only 1-vinylsilatrane exists in the etching solution of Comparative Example 2, due to its poor solubility, it cannot protect the SiO 2 layer.

[0067] In the etching solution of Comparative Example 3, only triethanolamine phosphate is added. Since the substances protecting silicon oxide and polysilicon are not contained, the etching rates of silicon oxide and polysilicon are relatively fast; triethanolamine phosphate can accelerate the etching rate of silicon nitride to a certain extent by partially decomposing the etching by-products of silicon nitride, but at the same time, part of triethanolamine phosphate is consumed during the decomposition of the etching by-products of silicon oxide. Therefore, the etching effect of silicon nitride is slightly different from that of the embodiment.

[0068] A further comparison and explanation are made through the accompanying drawings of the specification:

[0069] From Figure 1 it can be seen that the absorption peak at around 3380 cm -1 is the -OH absorption peak, the absorption peak at around 1100 cm -1 is the Si-O bond absorption peak, the absorption peak at around 1650 cm -1 is the C=C bond absorption peak, the absorption peaks at around 1000 cm -1 and 1050 cm -1 are the P=O and P-O bond absorption peaks, and the absorption peak at around 890 cm -1 is the Si-C bond absorption peak, indicating that the phosphosilicate ester with the structure of Formula 1 is successfully prepared in Example 1 of the present invention.

[0070] The present invention has been described exemplarily above in combination with the embodiments and the drawings. Obviously, the implementation of the present invention is not limited by the above-mentioned manner. As long as various improvements are made by adopting the method concept and technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A highly selective, low-corrosive silicon nitride etching solution, characterized in that: The etching solution comprises, in parts by weight, 2-5 parts of a product obtained by reacting 1-vinyl azasiltriane with 0.8-10 parts of pyrophosphoric acid, 75-90 parts of concentrated phosphoric acid, and 12-16 parts of ultrapure water; The mass ratio of 1-vinyl azasilatriane to pyrophosphoric acid is (3-5): (3.5-4.5); The method for preparing the highly selective and low-corrosive silicon nitride etching solution comprises the following steps: Step 1: Stir pyrophosphoric acid and 1-vinyl silane at 70-90 °C for 2 h; Step 2: After the above reaction is completed, cool to room temperature, add concentrated phosphoric acid and ultrapure water to the solution of step 1, and continue to stir and mix to obtain the silicon nitride etching solution.

2. The highly selective, low-corrosive silicon nitride etching solution according to claim 1, characterized in that: The ultrapure water is deionized water with a resistance of ≥ 18 MΩ.

3. A method for etching a 3D flash memory chip using the silicon nitride etching solution according to claim 1 or 2, characterized in that: The steps include: Step 1: Soak the silicon nitride sample in an etching device containing silicon nitride etching solution at 157°C-160°C. The soaking time is determined according to the thickness required for etching. Step 2: Rinse the soaked silicon nitride sample in ultrapure water at least twice, thus completing the silicon nitride wafer rinsing step; Step 3: Quickly dry the surface with a nitrogen gun.

4. The method for etching a 3D flash memory chip using silicon nitride etching solution according to claim 3, characterized in that: The etching apparatus in step 1 is sealed.

5. Use of the silicon nitride etching solution according to claim 1 or 2 in the field of 3D flash memory chips.

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