A phosphoric acid-based etching solution and its preparation method

Abstract

The present invention provides a phosphoric acid-based etching solution and a preparation method thereof. A phosphoric acid-based etching solution, the main components of which include 50-88% of phosphoric acid, 0.005-2% of an additive, and the balance being water, by weight of the total etching solution. By using the composition and type of the novel additive, the present invention significantly inhibits the combination of Si 2+ with the wafer surface, inhibits the formation of the SiO2 regeneration layer, and improves the service life of the phosphoric acid-based etching solution.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor technology, and particularly relates to a phosphoric acid-based etching solution and a preparation method thereof. Background Art

[0002] Since the planar structure of NAND, i.e., 2D NAND, cannot be extended infinitely in the plane and it is impossible to achieve high storage density, 3D NAND has been invented. Based on the development of 3D NAND technology, there are 16-layer, 32-layer, 64-layer, 128-layer and other 3D NANDs. In theory, the number of layers of 3D NAND can be stacked infinitely. Therefore, to increase the capacity of NAND and reduce costs, manufacturers do not need to invest a large amount in improving the manufacturing process. They only need to stack more layers to ensure the capacity, performance and reliability of 3D NAND flash memory.

[0003] The main basic structure of 3D NAND is an alternating stacked structure of Si3N4 and SiO2. During the etching of Si3N4 and SiO2 with phosphoric acid, the Si3N4 layer will be completely etched away and SiO2 will be retained. During the etching process, as the concentration of Si 2+ in the etching solution increases, the high-concentration Si 2+ will combine with the retained layer SiO2 to generate a regenerated SiO2 layer at the contact surface. The regenerated layer will seriously affect the size of the retained layer and cause the yield of the manufacturing process to decrease. Summary of the Invention

[0004] The present invention provides a phosphoric acid-based etching solution and a preparation method thereof. For the phosphoric acid-based etching solution, in the 3D NAND etching process, the combination of Si 2+ with the retained layer SiO2 can be inhibited, and the generation of the regenerated layer can be avoided.

[0005] The technical solution of the present invention is a phosphoric acid-based etching solution, which is characterized in that: the components of the etching solution include 50-88% by weight of phosphoric acid, 0.005-2% of an additive, and the balance is water.

[0006] Further, the phosphoric acid is electronic-grade phosphoric acid with a concentration ≥ 85% and a metal ion content ≤ 20 ppb.

[0007] Further, the additive is one or a mixture of several of polyoxyethylene dodecylamine, polyoxyethylene diamine, N-alkyl dimethyl ammonium chloride, N-alkyl dimethyl amine oxide, polyoxypropylene methyl ammonium chloride, polyoxypropylene block-based ammonium chloride or dialkyl dimethyl ammonium chloride.

[0008] Further, the water is ultrapure water with a resistivity of 15-18 MΩ*cm at 25°C.

[0009] The present invention also relates to a preparation method of the etching solution, and the specific steps are as follows:

[0010] S1. First, mix the additive with a part of ultrapure water and stir evenly to obtain an additive solution A;

[0011] S2. Add the additive solution A to a part of electronic-grade phosphoric acid, stir while adding, and after stirring evenly, let it stand for aging and then reserve it;

[0012] S3. Add the remaining electronic-grade phosphoric acid and the remaining ultrapure water to the material liquid obtained in S2 and stir evenly to obtain a phosphoric acid-based etching solution.

[0013] The present invention also relates to a preparation method of the etching solution, characterized in that: the aging time after mixing in S2 is 24 - 30h.

[0014] The present invention also relates to the application of the etching solution in the 3D NAND etching process.

[0015] The present invention has the following beneficial effects:

[0016] The additive used in the etching solution of the present invention can form a single-molecule isolation layer on the surface of the SiO2 layer, separating Si in the etching solution from the SiO2 layer, so that Si cannot contact the SiO2 layer, thereby inhibiting the formation of the regenerated layer of the SiO2 layer. After the etching process is completed, the single-molecule layer can be removed through processes such as cleaning with a cleaning solution. 2+ from the SiO2 layer, so that Si 2+ cannot contact the SiO2 layer, and further inhibits the formation of the regenerated layer of the SiO2 layer. After the etching process is completed, the single-molecule layer can be removed through processes such as cleaning with a cleaning solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is the basic structure of 3D NAND.

[0018] Figure 2 is a schematic diagram of the regenerated layer of the SiO2 layer.

[0019] Figure 3 is the schematic diagram of the action principle during the etching process. DETAILED DESCRIPTION OF THE INVENTION

[0020] The following will describe the implementation scheme of the present invention in detail in conjunction with the embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention.

[0021] In the following embodiments, the electronic-grade phosphoric acid used is BV III grade, and the international standard is SME I-C7 level.

[0022] Example 1

[0023] A phosphoric acid-based etching solution is prepared by the following method:

[0024] (1) By mass percentage of raw materials: 85% electronic-grade phosphoric acid, 0.2% polyoxyethylene dodecylamine, and the balance is ultrapure water. (2) First, mix polyoxyethylene dodecylamine with 50% of the total amount of ultrapure water and stir evenly for standby.

[0025] (3) Slowly add the mixed solution in step (2) to 50% of the total mass of electronic-grade phosphoric acid, stir while adding, and let it stand for more than 24 hours for standby after stirring evenly.

[0026] (4) Add the remaining electronic-grade phosphoric acid and ultrapure water to (3) and stir evenly to prepare a phosphoric acid-based etching solution.

[0027] Example 2

[0028] A phosphoric acid-based etching solution is prepared by the following method:

[0029] (1) By mass percentage of raw materials: 85% electronic-grade phosphoric acid, 0.4% polyoxyethylene dodecylamine, and the balance is ultrapure water. (2) First, mix polyoxyethylene dodecylamine with 50% of the ultrapure water and stir evenly for standby.

[0030] (3) Slowly add the mixed solution in step (2) to 50% of the total mass of electronic-grade phosphoric acid, stir while adding, and let it stand for more than 24 hours for standby after stirring evenly.

[0031] (4) Add the remaining electronic-grade phosphoric acid and ultrapure water to (3) and stir evenly to prepare a phosphoric acid-based etching solution.

[0032] Example 3

[0033] A phosphoric acid-based etching solution is prepared by the following method:

[0034] (1) By mass percentage of raw materials: 85% electronic-grade phosphoric acid, 0.8% polyoxyethylene dodecylamine, and the balance is ultrapure water. (2) First, mix polyoxyethylene dodecylamine with 50% of the ultrapure water and stir evenly for standby.

[0035] (3) Slowly add the mixed solution in step (2) to 50% of the total mass of electronic-grade phosphoric acid, stir while adding, and let it stand for more than 24 hours for standby after stirring evenly.

[0036] (4) Add the remaining electronic-grade phosphoric acid and ultrapure water to (3) and stir evenly to prepare a phosphoric acid-based etching solution.

[0037] Example 4

[0038] A phosphoric acid-based etching solution is prepared by the following method:

[0039] (1) By mass percentage of raw materials: 85% of electronic-grade phosphoric acid, 1.5% of polyoxyethylene dodecylamine, and the balance is ultrapure water. (2) First, mix polyoxyethylene dodecylamine with 50% of ultrapure water and stir evenly for later use.

[0040] (3) Slowly add the mixed solution in step (2) to 50% of the total mass of electronic-grade phosphoric acid, stir while adding, and let it stand for more than 24 hours for later use after stirring evenly.

[0041] (4) Add the remaining electronic-grade phosphoric acid and ultrapure water to (3) and stir evenly to prepare a phosphoric acid-based etching solution.

[0042] Example 5

[0043] A phosphoric acid-based etching solution is prepared by the following method:

[0044] (1) By mass percentage of raw materials: 85% of electronic-grade phosphoric acid, 2.2% of polyoxyethylene dodecylamine, and the balance is ultrapure water. (2) First, mix polyoxyethylene dodecylamine with 50% of ultrapure water and stir evenly for later use.

[0045] (3) Slowly add the mixed solution in step (2) to 50% of the total mass of electronic-grade phosphoric acid, stir while adding, and let it stand for more than 24 hours for later use after stirring evenly.

[0046] (4) Add the remaining electronic-grade phosphoric acid and ultrapure water to (3) and stir evenly to prepare a phosphoric acid-based etching solution.

[0047] Example 6

[0048] A phosphoric acid-based etching solution is prepared by the following method:

[0049] (1) By mass percentage of raw materials: 85% of electronic-grade phosphoric acid, 3.0% of polyoxyethylene dodecylamine, and the balance is ultrapure water. (2) First, mix polyoxyethylene dodecylamine with 50% of ultrapure water and stir evenly for later use.

[0050] (3) Slowly add the mixed solution in step (2) to 50% of the total mass of electronic-grade phosphoric acid, stir while adding, and let it stand for more than 24 hours for later use after stirring evenly.

[0051] (4) Add the remaining electronic-grade phosphoric acid and ultrapure water to (3) and stir evenly to prepare a phosphoric acid-based etching solution.

[0052] Example 7

[0053] The method steps are the same as those in Example 6, except that the additive is 1.5% of polyoxyethylene diamine.

[0054] Example 8

[0055] The method steps are the same as those in Example 6, except that the additive is 1.5% of N-dodecyldimethylammonium chloride added.

[0056] Example 9

[0057] The method steps are the same as those in Example 6, except that the additive is 1.5% of N-dodecyldimethylamine oxide added.

[0058] Example 10

[0059] The method steps are the same as those in Example 6, except that the additive is 1.5% of polyoxypropylene methyl ammonium chloride added.

[0060] Example 11

[0061] The method steps are the same as those in Example 6, except that the additive is 1.5% of polyoxypropylene block-based ammonium chloride added.

[0062] Example 12

[0063] The method steps are the same as those in Example 6, except that the additive is 1.5% of dialkyldimethylammonium chloride added.

[0064] Example 13

[0065] The method steps are the same as those in Example 6, except that the additives are 0.75% of polyoxyethylene dodecylamine and 0.75% of polyethylene polyoxyethylene diamine added.

[0066] Example 14

[0067] The method steps are the same as those in Example 6, except that the additives are 1.0% of polyoxyethylene dodecylamine and 0.5% of polyoxyethylene diamine added.

[0068] Example 15

[0069] The method steps are the same as those in Example 6, except that the additives are 0.5% of polyoxyethylene dodecylamine and 1.0% of polyoxyethylene diamine added.

[0070] Example 16

[0071] The method steps are the same as those in Example 6, except that the additives are 0.75% of polyoxyethylene dodecylamine and 0.75% of N-dodecyldimethylammonium chloride added.

[0072] Example 17

[0073] The method steps are the same as those in Example 6, except that the additives are 1.0% of polyoxyethylene dodecylamine and 0.5% of N-dodecyldimethylammonium chloride added.

[0074] Example 18

[0075] The method steps are the same as those in Example 6, except that the additives are 0.5% polyoxyethylene dodecylamine and 1.0% N-dodecyl dimethyl ammonium chloride.

[0076] Example 19

[0077] The method steps are the same as those in Example 6, except that the additives are 0.75% polyoxyethylene dodecylamine and 0.75% N-dodecyl dimethyl amine oxide.

[0078] Example 20

[0079] The method steps are the same as those in Example 6, except that the additives are 1.0% polyoxyethylene dodecylamine and 0.5% N-dodecyl dimethyl amine oxide.

[0080] Example 21

[0081] The method steps are the same as those in Example 6, except that the additives are 0.5% polyoxyethylene dodecylamine and 1.0% N-dodecyl dimethyl amine oxide.

[0082] Example 22

[0083] The method steps are the same as those in Example 6, except that the additives are 0.75% polyoxyethylene dodecylamine and 0.75% polyoxypropylene methyl ammonium chloride.

[0084] Example 23

[0085] The method steps are the same as those in Example 6, except that the additives are 1.0% polyoxyethylene dodecylamine and 0.5% polyoxypropylene methyl ammonium chloride.

[0086] Example 24

[0087] The method steps are the same as those in Example 6, except that the additives are 0.5% polyoxyethylene dodecylamine and 1.0% polyoxypropylene methyl ammonium chloride.

[0088] Example 25

[0089] The method steps are the same as those in Example 6, except that the additives are 0.75% polyoxyethylene dodecylamine and 0.75% polyoxypropylene block ammonium chloride.

[0090] Example 26

[0091] The method steps are the same as those in Example 6, except that the additives are 1.0% polyoxyethylene dodecylamine and 0.5% polyoxypropylene block ammonium chloride.

[0092] Example 27

[0093] The method steps are the same as those in Example 6, except that the additives are 0.5% polyoxyethylene dodecylamine and 1.0% polyoxypropylene block ammonium chloride.

[0094] Example 28

[0095] The method steps are the same as those in Example 6, except that the additives are 0.75% polyoxyethylene dodecylamine and 0.75% dialkyldimethylammonium chloride.

[0096] Example 29

[0097] The method steps are the same as those in Example 6, except that the additives are 1.0% polyoxyethylene dodecylamine and 0.5% dialkyldimethylammonium chloride.

[0098] Example 30

[0099] The method steps are the same as those in Example 6, except that the additives are 0.5% polyoxyethylene dodecylamine and 1.0% dialkyldimethylammonium chloride.

[0100] Example experimental method:

[0101] In a dust-free experiment, a 12-inch Si3N4 silicon wafer was taken. After cleaning the surface of Si3N4 with dilute hydrofluoric acid and ultrapure water, it was dried with high-purity nitrogen and reserved. By calculation, a quantitative Si3N4 silicon wafer was completely etched in a quantitative phosphoric acid etching solution, so that the concentration of the quantitative phosphoric acid etching solution Si 2+ reached a specific value. The actual value was measured using ICP-MS and the variation was calculated. The etching and measurement processes were repeated to obtain a phosphoric acid etching solution with a specific Si 2+ concentration. Through the above method, phosphoric acid etching solutions with Si 2+ concentrations of 80 ppm, 100 ppm, 120 ppm, 140 ppm, 160 ppm, and 180 ppm could be respectively prepared (in Examples 1-30). A 12-inch SiO2 silicon wafer was taken, evenly cut into 2×2 cm size, and after cleaning the surface of SiO2 with dilute hydrofluoric acid and ultrapure water, it was dried with high-purity nitrogen and reserved. A quantitative amount of the above-prepared phosphoric acid-based etching solution was placed in a quartz beaker and heated to 160 °C. Through an automatic temperature control and automatic water replenishment device, the temperature of the etching solution was maintained at 160 ± 0.5 °C, and the phosphoric acid concentration was maintained at 85.5 ± 0.5%. The initial thickness of the SiO2 layer was measured using an ellipsometer. After etching for 10 minutes, it was taken out, cleaned with ultrapure water, and dried with high-purity nitrogen. The thickness of the SiO2 layer after etching was measured using an ellipsometer. The comparison results of the experimental data in the above examples are shown in Table 1 below.

[0102] Table 1

[0103]

[0104]

[0105] The data shown in the data table are the object of this experimental study, i.e., the thickness change of the SiO2 layer after etching. The data in the table show that in the examples, the Si 2+ concentration of the additive within a certain range can significantly inhibit the formation of the regenerated layer of the SiO2 layer.

[0106] Obviously, the above examples and comparative examples are only examples for clear demonstration and are not limited to the above examples only. For those skilled in the art, there are very many variations or combinations of the above examples, and it is not necessary and impossible to list all the examples here. Therefore, the variations or changes based on the above examples are still within the protection scope of this invention.

Claims

1. Application of a phosphoric acid-based etching solution in a 3D NAND etching process, characterized in that: The composition of the etching solution includes phosphoric acid accounting for 50 - 88% of the total weight of the etching solution, 0.005 - 2% of an additive, and the balance is water; the phosphoric acid is electronic-grade phosphoric acid with a concentration ≥ 85% and a metal ion content ≤ 20 ppb; the additive is one or a mixture of polyoxyethylene dodecylamine, polyoxyethylene diamine, N-alkyl dimethyl ammonium chloride, N-alkyl dimethyl amine oxide, polyoxypropylene methyl ammonium chloride, polyoxypropylene block-based ammonium chloride, or dialkyl dimethyl ammonium chloride.

2. The application according to claim 1, wherein: The water is ultrapure water with a resistivity of 15 - 18 MΩ*cm at 25 °C.

3. The application according to claim 1, characterized in that: The specific steps for preparing the etching solution are as follows: S1. First, mix the additive with a part of the ultrapure water and stir evenly to obtain an additive solution A. S2. Add the additive solution A to a part of the electronic-grade phosphoric acid, stir while adding, and after stirring evenly, let it stand and age for later use. S3. Add the remaining electronic-grade phosphoric acid and the remaining ultrapure water to the material obtained in S2 and stir evenly to obtain a phosphoric acid-based etching solution.

4. The application according to claim 3, characterized in that: The aging time after mixing in S2 is 24 - 30 h.

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