3D NAND deep hole structure etching solution and preparation method and application thereof

Abstract

The invention discloses a 3D NAND deep hole structure etching solution as well as a preparation method and application thereof. The etching solution is prepared from the following raw materials in percentage by mass: 1 to 5 percent of polybasic acid dimethyl ester, 58 to 80 percent of phosphoric acid, 1 to 7 percent of depth-to-width ratio improver, 1 to 8 percent of stabilizer and the balance of water. The depth-to-width ratio improver is one or a combination of more of etidronic acid, hydroxyethylphosphonic acid, ibandronic acid, alendronic acid, acetic acid, phytic acid and pamidronic acid; the stabilizer is fluoboric acid and / or oxalic acid. According to the etching solution prepared by the invention, the top etching rate can be equal to the bottom etching rate, so that vertical parallel etching is performed on the 3D NAND storage chip to obtain a vertical deep hole structure, the storage density of the 3D NAND storage chip is improved, the electrical performance is ensured to be stable, the production yield is improved, and the application scene of the 3D NAND storage chip is expanded.

Description

Technical Field

[0001] This invention belongs to the field of electronic chemicals technology, specifically relating to a 3D NAND deep hole structure etching solution, its preparation method, and its application. Background Technology

[0002] 3D NAND is a non-volatile memory technology that retains stored data even after power loss. It overcomes the capacity limitations of 2D NAND and can scale to higher densities without sacrificing data integrity. 3D NAND uses multiple vertically stacked layers to achieve higher density, lower power consumption, better durability, faster read / write speeds, and lower cost. Because so many vertical cells are packaged into smaller width and length dimensions, 3D NAND has a larger capacity than 2D NAND in the same length and width dimensions. Therefore, 3D NAND has been widely used in enterprise-grade solid-state drives (SSDs) for data centers and servers. Since 3D NAND technology vertically stacks multiple layers of data storage cells, accommodating more storage cells in a smaller space, its manufacturing process has progressed from 128 layers to stacked structures of over 300 layers. When the aspect ratio of the stacked structure exceeds a certain value, plasma etching cannot achieve a vertical etching state at the bottom of the deep hole structure, thus affecting chip performance. In deep hole etching, most etching solutions can only achieve a bottom-wide, top-narrow etching morphology, and very few solutions can achieve parallel etching from top to bottom. However, with the increasing number of Si3N4 / SiO2 multilayers in the development of 3D NAND, the deep hole morphology has an increasingly greater impact on the performance of flash memory chips, thus placing higher demands on the etching of deep hole structures in 3D NAND.

[0003] Chinese patent CN118995226A discloses a 3D NAND deep hole structure etching solution, which is composed of 58-80% organic alcohols, 0.5-20% hydrofluoric acid, 0.5-4.5% silane coupling agent and ultrapure water (balance). It can etch 3D NAND deep hole structures with an aspect ratio of 100-1000, preferably 500-2000, and obtain an etching solution with a narrow top and wide bottom morphology, and the difference in etching width between the upper and lower layers exceeds 50%.

[0004] Chinese patent CN115894077B discloses a selective etching solution for 3D NAND structure wafers, comprising 1.5-2.0% silane additive 1 (one of 3-glycidyloxypropyltrimethoxysilane, diethoxy(3-glycidyloxypropyl)methylsilane, and triethoxy(3-glycidyloxypropyl)silane), 2.0-2.5% silane additive 2 (one of 2-cyanoethyltriethoxysilane, isocyanate-propyltriethoxysilane, and ureapropyltriethoxysilane), 83-86% phosphoric acid, and the balance being water. It exhibits etching selectivity for both silicon oxide and silicon nitride films, selectively removing silicon nitride films, extending the etching solution life, and adapting to the etching of multilayer structures.

[0005] However, as the number of layers in 3D NAND increases and the aspect ratio becomes larger, using an etchant with a narrow top and wide bottom often leads to tilted or offset vias. This prevents vias from penetrating all stacked layers and causes interference between adjacent via structures, rendering some stacked layers unusable and directly reducing storage density. Furthermore, non-vertical via structures can cause uneven linewidth due to channel tilt, increasing parasitic resistance and capacitance in the circuitry, thus affecting current transmission, increasing power consumption, and reducing adaptability. Therefore, it is necessary to provide an etchant capable of performing parallel top-to-bottom etching for 3D NAND. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a 3D NAND deep hole structure etching solution, its preparation method, and its application. This solution enables parallel etching from top to bottom, thereby solving the problem of deep hole tilting or shifting after etching. It allows the vias to penetrate all stacked layers and avoids mutual interference between adjacent deep hole structures, thus improving the yield of 3D NAND.

[0007] To achieve the above objectives, the present invention provides a 3D NAND deep hole structure etching solution, comprising the following raw materials by mass percentage: 1-5% dimethyl polycarboxylate, 58-80% phosphoric acid, 1-7% aspect ratio improver, 1-8% stabilizer, and the balance being water.

[0008] Preferably, the dimethyl polycarboxylate is one or a combination of dimethyl phosphate, dimethyl carbonate, dimethyl sulfate, and dimethyl colloid.

[0009] Preferably, the phosphoric acid has a mass concentration of 80-90% and the metal ion concentration is ≤200 ppb.

[0010] Preferably, the aspect ratio improver is one or a combination of several of etidronic acid, hydroxyethylphosphonic acid, ibandronic acid, alendronic acid, acetic acid, phytic acid, and pamidronic acid.

[0011] Preferably, the stabilizer is fluoroboric acid and / or oxalic acid.

[0012] Preferably, the water is ultrapure water with a resistivity of 15-18 MΩ*cm at 25°C.

[0013] This invention also provides a method for preparing a 3D NAND deep-hole structure etching solution, comprising the following steps: (1) Mix dimethyl polycarboxylate with water to obtain a hydrolysate solution; (2) Add the stabilizer to phosphoric acid and mix well to obtain mixture I; (3) Add the aspect ratio improver to mixture I and mix well to obtain mixture II; (4) Add the hydrolysate to the mixture II and mix well to obtain the 3D NAND deep hole structure etching solution.

[0014] The present invention also provides an application of a 3D NAND deep hole structure etching solution, wherein the application is in a deep hole structure.

[0015] Preferably, the aspect ratio of the deep hole structure is 500-2000.

[0016] Preferably, in the application, the etching conditions are an etching temperature of 25℃±0.5℃ and an etching time of 10-25min.

[0017] The beneficial effects of this invention are as follows: 1. Adding dimethyl polycarboxylate to the etching solution allows part of it to bind with the precipitated silicic acid in the solution, preventing silicic acid agglomeration and improving its diffusion performance in the deep hole structure; another part binds with silanol groups on the surface, preventing the reaction products from inhibiting the etching, ensuring that the deep hole structure is etched vertically and horizontally, and finally obtaining a deep hole structure that does not shift vertically.

[0018] 2. Using an aspect ratio improver, the decomposition of oxalic acid during etching generates a large number of bubbles, which carry the etching byproducts out from the bottom, thereby improving the aspect ratio.

[0019] 3. The present invention adds a stabilizer to the etching solution, which can effectively increase the solubility of organic additives, improve the smoothness of the surface after etching, prevent particle precipitation, and reduce the number of residual particles on the etched surface.

[0020] 4. The 3D NAND deep-hole structure etching solution prepared by this invention exhibits an initial etching rate greater than 9 A / min for silicon oxide wafers and greater than 5 A / min for silicon nitride wafers. When etching 3D NAND structure layers with deep holes (aspect ratio of 500-2000), it can etch a complete and uniform structure with an upper and lower layer etching width approaching 100%, achieving vertical etching. This allows the etched vias to penetrate all stacked layers and avoids mutual interference with adjacent deep holes. This meets the connectivity and electrical performance requirements of high aspect ratio 3D NAND, significantly improving production yield and thus enabling wider applications. Detailed Implementation

[0021] The technical solution of the present invention will be further explained and described below with reference to specific embodiments. It is worth noting that the following embodiments are only preferred embodiments of the present invention and should not be construed as limiting the present invention. The scope of protection of the present invention should be determined by the contents of the claims. Modifications and substitutions made by those skilled in the art to the technical solution of the present invention without creative effort all fall within the scope of protection of the present invention.

[0022] The preparation method is the same as in Example 1.

[0023] Comparative Example 5 An etching solution for 3D NAND flash memory comprises the following raw materials by mass percentage: 78% phosphoric acid (85%), 5% dimethyl phosphate, 6% hydrochloric acid, 8% fluoroboric acid, and the remainder being ultrapure water. The preparation method is the same as in Example 1.

[0024] Comparative Example 6 An etching solution for 3D NAND flash memory comprises the following raw materials by mass percentage: 78% phosphoric acid (85%), 5% dimethyl phosphate, 10% ibandronic acid, 8% fluoroboric acid, and the remainder being ultrapure water. The preparation method is the same as in Example 1.

[0025] Comparative Example 7 An etching solution for 3D NAND flash memory comprises the following raw materials by mass percentage: 78% phosphoric acid (85%), 8% dimethyl phosphate, 6% ibandronic acid, 8% fluoroboric acid, and the remainder being ultrapure water. The preparation method is the same as in Example 1.

[0026] Comparative Example 8 An etching solution for 3D NAND flash memory comprises the following raw materials by mass percentage: 78% phosphoric acid (85%), 8% fluoroboric acid, and the remainder being ultrapure water; The preparation method is the same as in Example 1.

[0027] Example 1 A 3D NAND deep hole structure etching solution comprises the following raw materials by mass percentage: 78% phosphoric acid (85% by mass), 5% dimethyl phosphate, 6% pamidronic acid, 8% fluoroboric acid, and the remainder being ultrapure water. The preparation method is as follows: (1) Mix dimethyl polycarboxylate with water to obtain a hydrolysate solution; (2) Add the stabilizer to phosphoric acid and mix well to obtain mixture I; (3) Add the aspect ratio improver to mixture I and mix well to obtain mixture II; (4) Add the hydrolysate to the mixture II and mix well to obtain the 3D NAND deep hole structure etching solution.

[0028] Example 2 A 3D NAND deep hole structure etching solution comprises the following raw materials by mass percentage: 78% phosphoric acid (85% by mass), 5% dimethyl phosphate, 6% etidronic acid, 8% fluoroboric acid, and the remainder is water and ultrapure water. The preparation method is the same as in Example 1.

[0029] Example 3 A 3D NAND deep hole structure etching solution comprises the following raw materials by mass percentage: 78% phosphoric acid (85% by mass), 5% dimethyl phosphate, 6% hydroxyethylphosphonic acid, 8% fluoroboric acid, and the remainder is water and ultrapure water. The preparation method is the same as in Example 1.

[0030] Example 4 A 3D NAND deep hole structure etching solution comprises the following raw materials by mass percentage: 78% phosphoric acid (85% by mass), 5% dimethyl phosphate, 6% ibandronic acid, 8% fluoroboric acid, and the remainder is water and ultrapure water. The preparation method is the same as in Example 1.

[0031] Example 5 A 3D NAND deep hole structure etching solution comprises the following raw materials by mass percentage: 78% phosphoric acid (85% by mass), 5% dimethyl phosphate, 6% alendronic acid, 8% fluoroboric acid, and the remainder is water and ultrapure water. The preparation method is the same as in Example 1.

[0032] Example 6 A 3D NAND deep hole structure etching solution comprises the following raw materials by mass percentage: 78% phosphoric acid (85% by mass), 5% dimethyl phosphate, 6% acetic acid, 8% fluoroboric acid, and the remainder is water and ultrapure water. The preparation method is the same as in Example 1.

[0033] Example 7 A 3D NAND deep hole structure etching solution comprises the following raw materials by mass percentage: 78% phosphoric acid (85% by mass), 5% dimethyl carbonate, 6% phytic acid, 8% fluoroboric acid, and the remainder is water and ultrapure water. The preparation method is the same as in Example 1.

[0034] Example 8 A 3D NAND deep hole structure etching solution comprises the following raw materials by mass percentage: 78% phosphoric acid (85% by mass), 5% dimethyl carbonate, 6% phytic acid, 8% fluoroboric acid, and the remainder is water and ultrapure water. The preparation method is the same as in Example 1.

[0035] Example 9 A 3D NAND deep hole structure etching solution comprises the following raw materials by mass percentage: 80% phosphoric acid (85% by mass), 5% dimethyl methacrylate, 6% ibandronic acid, 8% oxalic acid, and the remainder is water and ultrapure water. The preparation method is the same as in Example 1.

[0036] Example 10 A 3D NAND deep hole structure etching solution comprises the following raw materials by mass percentage: 78% phosphoric acid (85% by mass), 5% dimethyl sulfate, 6% ibandronic acid, 8% fluoroboric acid, and the remainder is water and ultrapure water. The preparation method is the same as in Example 1.

[0037] Comparative Example 1 An etching solution for 3D NAND flash memory comprises the following raw materials by mass percentage: 5% dimethyl phosphate, 6% ibandronic acid, 8% fluoroboric acid, and the remainder being ultrapure water; the preparation method is to add ibandronic acid and fluoroboric acid sequentially to water and mix them thoroughly.

[0038] Comparative Example 2 An etching solution for 3D NAND flash memory comprises the following raw materials by mass percentage: 78% phosphoric acid (85%), 5% dimethyl phosphate, 6% ibandronic acid, and the remainder being ultrapure water. The preparation method is the same as in Example 1.

[0039] Comparative Example 3 An etching solution for 3D NAND flash memory comprises the following raw materials by mass percentage: 78% phosphoric acid (85%), 5% dimethyl phosphate, 8% fluoroboric acid, and the remainder being ultrapure water. The preparation method is the same as in Example 1.

[0040] Comparative Example 4 An etching solution for 3D NAND flash memory comprises the following raw materials by mass percentage: 78% phosphoric acid (85%), 6% ibandronic acid, 8% fluoroboric acid, and the remainder being ultrapure water; The preparation method is the same as in Example 1.

[0041] Comparative Example 5 An etching solution for 3D NAND flash memory comprises the following raw materials by mass percentage: 78% phosphoric acid (85%), 5% dimethyl phosphate, 6% hydrochloric acid, 8% fluoroboric acid, and the remainder being ultrapure water. The preparation method is the same as in Example 1.

[0042] Comparative Example 6 An etching solution for 3D NAND flash memory comprises the following raw materials by mass percentage: 78% phosphoric acid (85%), 5% dimethyl phosphate, 10% ibandronic acid, 8% fluoroboric acid, and the remainder being ultrapure water. The preparation method is the same as in Example 1.

[0043] Comparative Example 7 An etching solution for 3D NAND flash memory comprises the following raw materials by mass percentage: 78% phosphoric acid (85%), 8% dimethyl phosphate, 6% ibandronic acid, 8% fluoroboric acid, and the remainder being ultrapure water. The preparation method is the same as in Example 1.

[0044] Comparative Example 8 An etching solution for 3D NAND flash memory comprises the following raw materials by mass percentage: 78% phosphoric acid (85%), 8% fluoroboric acid, and the remainder being ultrapure water; The preparation method is the same as in Example 1.

[0045] Etching experiments were conducted on silicon oxide and silicon nitride wafers on a silicon substrate (the silicon oxide wafers and silicon nitride wafers were cut into regular rectangles with a size of 1*2cm). Before etching, the oxide layer was removed by cleaning with a hydrofluoric acid solution and isopropanol solution with a volume ratio of 200:1 for 30s. Then, the wafers were placed in the etching solution prepared in the above examples and comparative examples for etching. The etching temperature was 25±0.5℃ and the etching time was 20min. The top etching amount and the bottom etching amount were recorded, and the etching rate and the ratio of the top and bottom etching widths were calculated. The results are shown in Table 1. The etching rate is calculated as follows: the thickness of silicon oxide and silicon nitride films before and after etching is detected using an elliptic polarization spectrometer, and the difference between the initial thickness and the thickness after a certain time is divided by the etching time to obtain the etching rate. Table 1 Etching effect

[0046] The results are shown in Table 1: In Examples 1-7, the addition of dimethyl polycarboxylate to the etching solution effectively ensured parallel etching of the deep hole structure, with an etching result close to 100%, significantly better than the comparative example without dimethyl polycarboxylate. Simultaneously, the use of an aspect ratio improver allowed for the generation of numerous bubbles during etching due to the decomposition of oxalic acid, which carried etching byproducts from the bottom, thus promoting parallel etching. Furthermore, when etching 3D NAND structure layers (500-2000 layers) with deep holes, a complete and uniform structure could be etched, with the etch width between the upper and lower layers approaching 100%, achieving vertical etching. This allowed the etched vias to penetrate all stacked layers and avoid mutual interference with adjacent deep holes, adapting to the connectivity and electrical performance requirements of high aspect ratio 3D NAND, significantly improving production yield, and thus enabling wider applications.

Claims

1. A 3D NAND deep-hole structure etching solution, characterized in that: The raw materials consist of the following components by weight percentage: 1-5% dimethyl polycarboxylate, 58-80% phosphoric acid, 1-7% aspect ratio improver, 1-8% stabilizer, and the balance being water.

2. The 3D NAND deep-hole structure etching solution according to claim 1, characterized in that: The dimethyl polycarboxylate is one or a combination of dimethyl phosphate, dimethyl carbonate, dimethyl sulfate, and dimethyl colloid.

3. The 3D NAND deep-hole structure etching solution according to claim 1, characterized in that: The phosphoric acid has a mass concentration of 80-90%, and the metal ion content is required to be ≤200 ppb.

4. The 3D NAND deep-hole structure etching solution according to claim 1, characterized in that: The aspect ratio improver is one or a combination of several of etidronic acid, hydroxyethylphosphonic acid, ibandronic acid, alendronic acid, acetic acid, phytic acid, and pamidronic acid.

5. The 3D NAND deep-hole structure etching solution according to claim 1, characterized in that: The stabilizer is fluoroboric acid and / or oxalic acid.

6. The 3D NAND deep-hole structure etching solution according to claim 1, characterized in that: The water is ultrapure water with a resistivity of 15-18 MΩ*cm at 25℃.

7. A method for preparing a 3D NAND deep-hole structure etching solution as described in any one of claims 1-6, characterized in that: Includes the following steps: (1) Mix dimethyl polycarboxylate with water to obtain a hydrolysate solution; (2) Add the stabilizer to phosphoric acid and mix well to obtain mixture I; (3) Add the aspect ratio improver to mixture I and mix well to obtain mixture II; (4) Add the hydrolysate to the mixture II and mix well to obtain the 3D NAND deep hole structure etching solution.

8. The application of the 3D NAND deep hole structure etching solution as described in any one of claims 1-6, characterized in that: The application is in deep hole structures.

9. The application according to claim 9, characterized in that: The aspect ratio of the deep hole structure is 500-2000.

10. The application according to claim 9, characterized in that: When applying the application, the etching conditions are an etching temperature of 25℃±0.5℃ and an etching time of 10-25min.

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