Molybdenum etching solution

Abstract

The invention provides a metal molybdenum etching solution which comprises the following components in percentage by mass: 0.5-2% of an oxidizing agent, 5-30% of a pH buffering agent, 0.1-5% of an ionic complexing agent, 0.1-3% of an aluminum oxide etching inhibitor and the balance of deionized water. The molybdenum etching solution disclosed by the invention can be used for carrying out rate-controllable etching on nano-scale metal molybdenum, no residue is left on the surface of the etched metal molybdenum, and the metal molybdenum and aluminum oxide have a relatively high selection ratio.

Description

Technical Field

[0001] The invention belongs to the field of electronic chemicals, and in particular relates to a technical solution of a molybdenum etching solution. Background Art

[0002] With the continuous advancement of cutting-edge technologies such as big data, cloud computing, the Internet of Things, and artificial intelligence, consumer electronics products are also rapidly iterating, resulting in an unprecedented demand for storage capacity in devices. 3D NAND flash memory technology has become one of the most popular storage solutions today due to its innovation in vertical stacking of storage cells, enabling higher storage capacity and excellent performance in a relatively limited space. In order to increase the storage capacity of 3D NAND, increasing the number of storage layers is a direct and effective strategy. However, as the number of storage layers increases, in order to maintain the overall height and solve the problems of image accuracy and stress management, the thickness of each layer must be reduced accordingly. This approach has raised new challenges: the reduction in the size of the unit storage cell may aggravate the electron scattering effect, thereby increasing the channel resistance, which in turn has a negative impact on the performance of the unit transistor. This effect is manifested in reduced transistor efficiency and longer programming and erasing times for products. Therefore, the use of metal molybdenum (Mo) with low resistivity, strong resistance to electromigration, and excellent transistor performance as a material to replace traditional metals (such as copper or tungsten) is the next goal of major memory manufacturers.

[0003] Aluminum oxide (Al2O3) is often used as Hi-k material in 3D NAND flash memory chips due to its high hardness, high temperature resistance, excellent chemical stability, and high dielectric constant. Generally speaking, the thickness of Hi-k material in 3D NAND flash memory chips is very thin, usually within 5nm. Traditional etching solutions have low selectivity for aluminum oxide during etching of molybdenum metal layers, which can easily damage the aluminum oxide structure, and more molybdenum oxide residues are left after etching. Summary of the invention

[0004] The present invention aims to solve the problems that the existing etching solution has low selectivity for aluminum oxide in the process of etching metal molybdenum, is easy to damage the aluminum oxide structure, and has a large amount of residual molybdenum oxide after etching. The present invention aims to provide a molybdenum etching solution which can perform rate-controllable etching on nanometer-scale metal molybdenum, has no residue on the surface of the metal molybdenum after etching, and has a high selectivity ratio between metal molybdenum and aluminum oxide.

[0005] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is: A molybdenum etching solution mainly comprises 0.5-2% by mass of an oxidant, 5%-30% by mass of a pH buffer, 0.1%-5% by mass of an ionic complexing agent, 0.1%-3% by mass of an aluminum oxide etching inhibitor, and the remaining component is deionized water.

[0006] In the above scheme, the oxidant is an oxidant with strong oxidizing property in a neutral solution, preferably one or a mixture of persulfate, ammonium persulfate, periodic acid, ammonium periodate, iodic acid, ammonium iodate, hypoiodous acid, hydrogen peroxide, and hypochlorous acid.

[0007] Slightly neutral refers to pH 4-10. This does not mean that the oxidants are slightly neutral, but that these oxidants have strong oxidizing properties even in a slightly neutral environment.

[0008] In the above scheme, the pH buffer is a group selected from the group consisting of diammonium phosphate / diammonium hydrogen phosphate buffer, acetic acid / ammonium acetate buffer, and acetic acid / diammonium hydrogen phosphate buffer.

[0009] In the above scheme, the ionic complexing agent is one or a mixture of tris(2-hydroxyethyl)methylammonium hydroxide, (2-hydroxyethyl)dimethyl(3-sulfopropyl)ammonium hydroxide inner salt, (3-(methacrylamido)propyl)dimethyl(3-thiopropyl)ammonium hydroxide inner salt, [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonatepropyl)ammonium hydroxide, (methoxycarbonylsulfamoyl)triethylammonium hydroxide, tetrakishydroxymethylphosphonium sulfate, and tetrakishydroxymethylphosphonium chloride.

[0010] In the above scheme, the aluminum oxide etching inhibitor is one or a mixture of boric acid, methylboric acid, 2-hydroxymethylphenylboric acid, p-methylphenylboric acid, 2,4,6-trimethylphenylboric acid, 3-methylphenylboric acid, 2-(trifluoromethyl)phenylboric acid, and 4-fluoro-3-methylphenylboric acid.

[0011] In the above scheme, the molybdenum etching solution is used to selectively etch molybdenum and selectively inhibit the etching of aluminum oxide.

[0012] The etching rate of molybdenum by the molybdenum etching solution is controllable within 5-100A / min, and no molybdenum oxide remains after etching.

[0013] In the above scheme, the etching selectivity ratio of the molybdenum etching solution to molybdenum and aluminum oxide is greater than 1000:1.

[0014] In the above solution, the aluminum oxide film layer is an amorphous aluminum oxide film layer deposited by ALD with a thickness of less than 10 nm.

[0015] In the above scheme, the pH value of the molybdenum etching solution is in the range of 4-5.5.

[0016] Beneficial effects of the present invention: (1) The molybdenum etching solution of the present invention is an aqueous system with low viscosity and high solubility of each component. The preparation of the solution will not cause the problem of slow dissolution and can ensure a low particle number level. When deep-hole nanoscale metal molybdenum etching is performed, no residual particles will remain in the solution. It is suitable for complex high-end chips with high aspect ratio and small size.

[0017] (2) The lone pair of electrons on the coordinating atoms of the ionic complexing agent in the molybdenum etching solution of the present invention easily forms a complex with the empty orbital of the metal molybdenum, and the ionic complexing agent contains N + or P + Charged atoms can generate charge interactions with hydronium ions in the solution, reducing the concentration of hydronium ions on the surface of metal molybdenum, thereby preventing the molybdenum oxide from being dissolved too quickly. Combined with the pH value of the solution, it can prevent residues and control the etching rate.

[0018] (3) The pH buffer system in the molybdenum etching solution of the present invention stabilizes the pH of the solution between 4 and 5.5. The stable pH provides a stable concentration of hydronium ions, thereby achieving stable control of the etching rate. Moreover, at a pH between 4 and 5.5, metallic molybdenum will not be passivated, and the formed oxide has good solubility.

[0019] (4) The boric acid-based aluminum oxide inhibitor in the molybdenum etching solution of the present invention can effectively inhibit the amorphous aluminum oxide deposited by ALD, thereby preventing excessive etching of the amorphous aluminum oxide deposited by ALD while etching metal molybdenum, thereby improving the etching selectivity of molybdenum to aluminum oxide.

[0020] (5) The oxidant in the molybdenum etching solution of the present invention is an oxidant with strong oxidizing properties even in a neutral environment. It can also oxidize metal molybdenum well in an etching solution environment with a pH value between 4 and 5.5, and will not cause etching problems of molybdenum due to insufficient oxidizing properties. DETAILED DESCRIPTION

[0021] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with the embodiments, but the content of the present invention is not limited to the following embodiments.

[0022] Examples 1-10 The contents of the components of the embodiments and comparative examples according to the present invention are listed in Table 1.

[0023] A molybdenum etching solution mainly comprises 0.5-2% by mass of an oxidant, 5%-30% by mass of a pH buffer, 0.1%-5% by mass of an ionic complexing agent, 0.1%-3% by mass of an aluminum oxide etching inhibitor, and the remaining component is deionized water.

[0024] The etching solution is prepared according to the following steps: 1. Weigh the required oxidant, pH buffer, ionic complexing agent, aluminum oxide etching inhibitor and the remaining water according to the formula mass fraction; 2. Add oxidant, pH buffer, ionic complexing agent and aluminum oxide etching inhibitor to water in sequence; 3. Stir at room temperature for 1 hour until the etching solution is evenly mixed. The etching solution is prepared and set aside.

[0025] Table 1

[0026] Etching experiments were conducted using various combinations of etching solutions according to the embodiments of the present invention. The etching process is as follows: Etching object: 450A metal molybdenum film and 80A amorphous aluminum oxide film Etching temperature: 30℃ Etching time: Etch the metal molybdenum film and the amorphous aluminum oxide film for 10 minutes and 100 minutes respectively. (If the etching rate is too fast, shorten the etching time accordingly) Etching rate measurement method: For the detection of metal molybdenum film thickness, a square resistance meter is used. The square resistance of the metal molybdenum film is measured using a four-point probe. The film thickness of the metal molybdenum is calculated by the resistivity of molybdenum. The etching rate is calculated by dividing the difference between the initial thickness and the thickness after etching by the etching time (minutes). For the film thickness detection of amorphous aluminum oxide, an ellipsometer is used. The film thickness of amorphous aluminum oxide is calculated by the optical path difference. The etching rate is calculated by dividing the difference between the initial thickness and the thickness after etching by the etching time (minutes). The selectivity represents the ratio of the etching rate of the metal molybdenum film to the etching rate of the aluminum oxide film.

[0027] Method for measuring residual molybdenum oxide: The above etching is performed using a structure sheet with nano-scale metal molybdenum, and the presence or absence of residual molybdenum oxide in the structure is observed by SEM.

[0028] The etching test results are listed in Table 2.

[0029] Table 2

[0030] Comparing the above embodiments with the comparative examples, the data show that the ionic complexing agent structure in the etching solution of the present invention has both a coordination group containing a lone pair of electrons and a N-containing + or P + Charged atoms can complex with metal molybdenum and reduce the concentration of hydronium ions on the surface of metal molybdenum, thereby preventing the molybdenum oxide from being dissolved too quickly, preventing residue and controlling the etching rate. Combined with boric acid-based aluminum oxide etching inhibitors, it can be very effective The etching rate of the etching solution on the amorphous aluminum oxide deposited by AlD is reduced, and the etching selectivity ratio of metal molybdenum and aluminum oxide is greater than 1000:1.

[0031] Obviously, the above embodiments are only examples for clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the protection scope of the invention.

Claims

1. A molybdenum etching solution, characterized in that The etching solution mainly comprises 0.5-2% by mass of an oxidant, 5%-30% by mass of a pH buffer, 0.1%-5% by mass of an ionic complexing agent, 0.1%-3% by mass of an aluminum oxide etching inhibitor, and the remaining component is deionized water.

2. A platinum etching solution according to claim 1, characterized in that, The oxidant is selected from one or a mixture of persulfuric acid, ammonium persulfate, periodic acid, ammonium periodate, iodic acid, ammonium iodate, hypoiodous acid, hydrogen peroxide, and hypochlorous acid.

3. A platinum etching solution according to claim 1, characterized in that, The pH buffer is selected from any one of diammonium phosphate / diammonium hydrogen phosphate buffers, acetic acid / ammonium acetate buffers, and acetic acid / diammonium hydrogen phosphate buffers.

4. A platinum etching solution according to claim 1, characterized in that, The ionic complexing agent is selected from one or a mixture of tris(2-hydroxyethyl)methylammonium hydroxide, (2-hydroxyethyl)dimethyl(3-sulfopropyl)ammonium hydroxide inner salt, (3-(methacrylamino)propyl)dimethyl(3-thiopropyl)ammonium hydroxide inner salt, [2-(methacryloxy)ethyl]dimethyl-(3-sulfonic acid propyl)ammonium hydroxide, (methoxycarbonylsulfamoyl)triethylammonium hydroxide or tetrakis(hydroxymethyl)phosphonium sulfate or tetrakis(hydroxymethyl)phosphonium chloride.

5. A platinum etching solution according to claim 1, characterized in that, The aluminum oxide etching inhibitor is one or a mixture of boric acid, methylboric acid, 2-hydroxymethylphenylboric acid, p-methylphenylboric acid, 2,4,6-trimethylphenylboric acid, 3-methylphenylboric acid, 2-(trifluoromethyl)phenylboric acid or 4-fluoro-3-methylphenylboric acid.

6. A platinum etching solution according to claim 1, characterized in that, The pH value of the molybdenum etching solution is between 4 and 5.

5.

7. Use of the platinum etching solution according to any one of claims 1 to 6 in selectively etching molybdenum and selectively inhibiting the etching of aluminum oxide.

8. The use according to claim 7, characterized in that: The etching rate of molybdenum by the molybdenum etching solution is controllable within 5-100A / min, and no molybdenum oxide remains after etching.

9. The use according to claim 8, characterized in that: The etching selectivity ratio of the molybdenum etching solution to molybdenum and aluminum oxide is greater than 1000:

1.

10. The use according to claim 7, characterized in that: The aluminum oxide film layer is an amorphous aluminum oxide film layer deposited by ALD with a thickness of less than 10 nm.

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