JP7803170B2 - Etching solution, etching method, and manufacturing method of semiconductor integrated circuit - Google Patents

Description

The present invention relates to an etching solution, an etching method, and a method for manufacturing semiconductor integrated circuits.

The manufacturing of semiconductor integrated circuits consists of multiple, varied processing steps. During the manufacturing process, various material depositions, lithography, etching, and other processes are repeated. The size of wiring and integrated circuits within semiconductor substrates becomes smaller every year, requiring higher processing precision in each process.

Copper wiring in semiconductor integrated circuits is also becoming increasingly miniaturized, but lithography misalignment during the formation of vertical wiring (vias) can shorten the distance between adjacent wiring, creating the problem of increased susceptibility to short circuits.

To solve this problem, a method called fully self-aligned via (FSAV) has been proposed, in which the copper wiring is slightly etched in advance, ensuring distance from adjacent wiring even if lithography misalignments occur. To achieve this method, an etching solution is required that can uniformly etch copper wiring on the nanometer order.

As etching solutions for etching copper, acidic etching solutions containing hydrogen peroxide are disclosed, such as in Patent Document 1 and Patent Document 2.

Japanese Patent Application Laid-Open No. 2016-135928 Japanese Patent Application Laid-Open No. 2020-079444

However, the etching solutions disclosed in Patent Documents 1 and 2 have the problem that the etching rate for different orientations of each copper crystal plane is not constant, resulting in the occurrence of unevenness (roughness) on the copper surface.

The present invention was made in consideration of these problems, and its object is to provide an etching solution that suppresses roughness on copper surfaces. It is also an object of the present invention to provide an etching method using the etching solution and a method for manufacturing semiconductor integrated circuits.

Previously, etching solutions containing various components have been investigated, but they have not been able to sufficiently suppress the roughness of copper surfaces. After extensive research, the inventors discovered the etching solution described below, which suppresses the roughness of copper surfaces.

That is, the gist of the present invention is as follows.
[1] An etching solution for etching copper or copper alloys, comprising a chelating agent (A) and substantially free of hydrogen peroxide.
[2] The etching solution according to [1], having a pH of 7 or more.
[3] The etching solution according to [1] or [2], having a pH of 9 to 12.
[4] The etching solution according to any one of [1] to [3], further comprising a pH adjuster (B).
[5] The etching solution according to any one of [1] to [4], further comprising a surfactant (C).
[6] An etching method comprising a step of etching copper or a copper alloy using the etching solution according to any one of [1] to [5].
[7] The etching method according to [6], wherein wiring formed on a substrate surface from copper or a copper alloy is etched.
[8] The etching method according to [7], wherein the spacing between the wirings is 100 nm or less.
[9] A method for manufacturing a semiconductor integrated circuit, comprising a step of etching copper or a copper alloy using the etching solution according to any one of [1] to [5].
[10] A method for manufacturing a semiconductor integrated circuit, comprising the etching method according to any one of [6] to [8].

The etching solution of the present invention suppresses roughness on the copper surface. Furthermore, the etching method of the present invention and the method for manufacturing a semiconductor integrated circuit of the present invention suppress roughness on the copper surface during the etching process.

The present invention is described in detail below, but is not limited to the following embodiments and can be implemented in various modifications within the scope of its gist. Furthermore, when the expression "~" is used in this specification, it is intended to include the numerical values or physical property values before and after it.

The etching solution for etching copper or copper alloys of the present invention (hereinafter sometimes referred to as the "etching solution of the present invention") contains a chelating agent (A) and is substantially free of hydrogen peroxide.

(Chelating Agent (A))
The etching solution of the present invention contains a chelating agent (A). The chelating agent (A) is a component that forms a chelate compound with metal ions and has the function of dissolving the metal. When the etching solution contains the chelating agent (A), the etching rate is excellent.

Examples of chelating agents (A) include oxalic acid, malonic acid, succinic acid, glutaric acid, phthalic acid, tartaric acid, citric acid, malic acid, isocitric acid, alanine, arginine, asparagine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, valine, iminodiacetic acid, hydroxyethyliminodiacetic acid, dihydroxyethylglycine, nitrilotriacetic acid, hydroxyethylethylenediaminetriacetic acid, ethylenediaminetetraacetic acid, 1,3-propanol ... Examples of suitable chelating agents (A) include propanediaminetetraacetic acid, 1,3-diamino-2-hydroxypropanetetraacetic acid, glycol ether diaminetetraacetic acid, ethylenediamine, N-methyl-ethylenediamine, 1,2-diaminopropane, 1,3-diaminopropane, 1,4-butanediamine, N-methyl-1,3-diaminopropane, diethylenetriaminepentaacetic acid, triethylenetetraaminehexaacetic acid, dicarboxymethylglutamic acid, (S,S)-ethylenediaminedisuccinoacetic acid, 1-hydroxyethane-1,1-diphosphonic acid, ethylenediaminetetra(methylenephosphonic acid), gluconic acid, and picolinic acid. These chelating agents (A) may be used alone or in combination. Among these chelating agents (A), aspartic acid, histidine, and ethylenediaminetetraacetic acid are preferred due to their excellent etching rate, with aspartic acid and histidine being more preferred.

The content of the chelating agent (A) is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and preferably 10% by mass or less, and more preferably 5% by mass or less, based on 100% by mass of the etching solution. When the content of the chelating agent (A) is 0.01% by mass or more, the etching solution has an excellent etching rate. When the content of the chelating agent (A) is 10% by mass or less, the etching solution is economical.

(pH adjuster (B))
The etching solution of the present invention preferably further contains a pH adjuster (B) in order to adjust the flatness and etching rate.

Examples of pH adjusters (B) include potassium hydroxide, ammonia, tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrabutylammonium hydroxide. These pH adjusters (B) may be used alone or in combination of two or more. Among these pH adjusters (B), tetraethylammonium hydroxide and potassium hydroxide are preferred due to their excellent flatness, and tetraethylammonium hydroxide is more preferred.

The content of pH adjuster (B) is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and preferably 10% by mass or less, more preferably 1% by mass or less, based on 100% by mass of the etching solution. When the content of pH adjuster (B) is 0.01% by mass or more, the etching solution has an excellent etching rate. When the content of pH adjuster (B) is 10% by mass or less, the etching solution is economical.

(Surfactant (C))
The etching solution of the present invention preferably further contains a surfactant (C) because it controls the etching shape by surface adsorption and provides excellent flatness.

Examples of surfactants (C) include alkylbenzenesulfonic acid, polyoxyethylene alkyl ether, polyoxyethylene alkyl ether sulfate, polyoxyethylene alkyl ether acetate, polyoxyethylene alkyl ether phosphate, polyoxyethylene alkylamine, alkylalkanolamide, alkylammonium salt, and alkylamine oxide. These surfactants (C) may be used alone or in combination of two or more. Among these surfactants (C), dodecylbenzenesulfonic acid, polyoxyethylene alkyl ether, and alkylammonium salt are preferred due to their excellent etching profile control, with polyoxyethylene alkyl ether and alkylammonium salt being more preferred.

The content of surfactant (C) is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and preferably 1.0% by mass or less, and more preferably 0.5% by mass or less, based on 100% by mass of the etching solution. When the content of surfactant (C) is 0.01% by mass or more, the etching solution has excellent etching shape controllability. When the content of surfactant (C) is 1.0% by mass or less, the etching solution has excellent low-foaming properties.

(Oxidizing Agent (D))
The etching solution of the present invention may further contain an oxidizing agent (D) because it oxidizes metals and has an excellent etching rate. However, the oxidizing agent (D) is substantially free of hydrogen peroxide. Hydrogen peroxide has different reaction rates for each crystal orientation of copper, and therefore hydrogen peroxide deteriorates the flatness after etching. "Substantially free" means that the content is less than 0.01% by mass, preferably 0.001% by mass or less, and more preferably 0% by mass, relative to 100% by mass of the etching solution.

Examples of the oxidizing agent (D) include periodic acid, hypochlorite, and benzoquinone. These oxidizing agents (D) may be used alone or in combination of two or more. Among these oxidizing agents (D), periodic acid and benzoquinone are preferred because of their excellent flatness.

The content of oxidizing agent (D) is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and preferably 10% by mass or less, more preferably 1% by mass or less, based on 100% by mass of the etching solution. When the content of oxidizing agent (D) is 0.01% by mass or more, the etching solution has an excellent etching rate. When the content of oxidizing agent (D) is 10% by mass or less, the etching solution is economical.

(Water (E))
The etching solution of the present invention preferably further contains water (E) because water can dissolve the above-mentioned components (A) to (D) and other components described below.

The content of water (E) is preferably 90% by mass or more, more preferably 95% by mass or more, and preferably 99.9% by mass or less, and more preferably 99.8% by mass or less, based on 100% by mass of the etching solution. When the content of water (E) is 90% by mass or more, the solubility of the above-mentioned components (A) to (D) and other components described below is excellent. When the content of water (E) is 99.9% by mass or less, the effects of the present invention are more easily achieved.

(Other ingredients)
The etching solution of the present invention may contain other components in addition to the chelating agent (A), the pH adjuster (B), the surfactant (C), the oxidizing agent (D), and the water (E).

Other components include, for example, solvents such as ethylene glycol, propylene glycol, polyvinyl alcohol, ethanol, 1-propanol, isopropyl alcohol, 1-butanol, 2-butanol, 2-methyl-1-propanol, 2-methyl-2-propanol, propylene glycol monomethyl ether, and propylene glycol monomethyl ether acetate; and polymers such as polyacrylic acid, polyacrylamide, dimethyl sulfoxide, polydiallyldimethylammonium chloride, polyethyleneimine, and poly(acrylamide-diallyldimethylammonium chloride) copolymer. These other components may be used alone or in combination of two or more.

The etching solution of the present invention preferably has a pH of 7 or higher, and more preferably a pH of 9 to 12, in order to achieve an excellent etching shape.

(mass ratio of components)
The mass ratio of the pH adjuster (B) to the chelating agent (A) (mass of pH adjuster (B)/mass of chelating agent (A)) is preferably 0.01 or more, more preferably 0.1 or more, and is preferably 100 or less, more preferably 10 or less. When the mass ratio of the pH adjuster (B) to the chelating agent (A) is 0.01 or more, the etching solution has excellent flatness. When the mass ratio of the pH adjuster (B) to the chelating agent (A) is 100 or less, the etching solution has an excellent metal etching rate.

The mass ratio of surfactant (C) to chelating agent (A) (mass of surfactant (C)/mass of chelating agent (A)) is preferably 0.01 or more, more preferably 0.1 or more, and preferably 10 or less, more preferably 5 or less. When the mass ratio of surfactant (C) to chelating agent (A) is 0.01 or more, the etching solution has excellent etching shape control. When the mass ratio of surfactant (C) to chelating agent (A) is 10 or less, the etching solution has excellent metal etching rate.

The mass ratio of surfactant (C) to pH adjuster (B) (mass of surfactant (C)/mass of pH adjuster (B)) is preferably 0.01 or more, more preferably 0.1 or more, and preferably 10 or less, more preferably 5 or less. When the mass ratio of surfactant (C) to pH adjuster (B) is 0.01 or more, the etching solution has excellent etching shape control. When the mass ratio of surfactant (C) to pH adjuster (B) is 10 or less, the etching solution has excellent metal etching rate.

(Method for producing etching solution)
The etching solution of the present invention can be produced by mixing the necessary components.
The order of mixing is not particularly limited, and all of the components may be mixed at once, or some of the components may be mixed in advance and then the remaining components may be mixed.
The etching solution of the present invention may be produced by preparing a highly concentrated etching solution and then diluting it to the desired concentration.

(Physical properties of etching solution)
The etching rate of the etching solution of the present invention for copper or copper alloy is preferably 0.5 nm/min or more, more preferably 1 nm/min or more, and preferably 20 nm/min or less, more preferably 10 nm/min or less. When the etching rate of the etching solution for copper or copper alloy is 0.5 nm/min or more, the etching solution has excellent productivity in the etching process. When the etching rate of the etching solution for copper or copper alloy is 20 nm/min or less, the etching solution has excellent controllability in the etching process.

The etching rate of the etching solution of the present invention for _SiO2 is preferably 0.1 nm/min or less, more preferably 0.01 nm/min or less. When the etching rate of the etching solution for _SiO2 is 0.1 nm/min or less, the etching solution has excellent controllability of the post-etching shape.

(Subject to be etched by etching solution)
The etching target of the etching solution of the present invention is not particularly limited as long as it is copper or a copper alloy, but the etching solution of the present invention is suitable for etching fine structures on the nanometer scale. The etching solution of the present invention is preferably used for semiconductor integrated circuits in which wiring made of copper or a copper alloy is present on the substrate surface, and is particularly suitable for semiconductor integrated circuits in which the wiring is present on the substrate surface at intervals of 100 nm or less.

The metal species is copper or a copper alloy, with copper being preferred.
The wiring interval is preferably 100 nm or less, and more preferably 50 nm or less.
The semiconductor integrated circuit is preferably a logic circuit, a DRAM circuit, a flash memory circuit, or an image sensor circuit.

(Etching Method)
The etching method of the present invention comprises the step of etching copper or a copper alloy using the etching solution of the present invention.

The etching method can be any known method, such as batch or single-wafer etching.

The temperature during etching is preferably 15° C. or higher, more preferably 20° C. or higher, since this can improve the etching rate for copper or copper alloys.
The temperature during etching is preferably 100° C. or less, more preferably 80° C. or less, from the viewpoint of reducing damage to the substrate and ensuring etching stability.

(Method for manufacturing semiconductor integrated circuits)
The method for producing a semiconductor integrated circuit of the present invention includes a step of etching copper or a copper alloy using the etching solution of the present invention.
The method for manufacturing a semiconductor integrated circuit of the present invention includes the etching method of the present invention.

(Application)
The etching solution and the etching method of the present invention can be suitably used in the manufacture of semiconductor integrated circuits, and because they provide excellent flatness after etching and can etch fine structures on the nanometer scale, they are preferably used in semiconductor integrated circuits in which wiring formed of copper or a copper alloy is present on the substrate surface, and are particularly suitably used in semiconductor integrated circuits in which the wiring is present on the substrate surface at intervals of 100 nm or less.

The present invention will be explained in more detail below using examples, but the present invention is not limited to the descriptions in the following examples as long as it does not deviate from the gist of the invention.

(raw materials)
In the examples and comparative examples, the following components were used.
Component (A1): Aspartic acid Component (A2): Histidine Component (A3): Citric acid Component (D'1): Hydrogen peroxide Component (E1): Water

(pH measurement)
The etching solutions obtained in the examples and comparative examples were each measured for pH using a pH meter (model name "D-74", manufactured by Horiba, Ltd.) while being stirred using a magnetic stirrer.

(Method for measuring etching rate)
A silicon substrate on which a copper film was formed by plating was cut into a 20 mm square. The substrate was then immersed in the etching solution obtained in the Examples and Comparative Examples at 25°C for 10 minutes. After immersion, the substrate was removed, and the copper concentration in the etching solution after immersion was measured using an ICP optical emission analyzer (model name "SPS1700HVR", manufactured by Seiko Instruments Inc.). From the measured copper concentration, the amount of copper eluted in 10 minutes was calculated and converted into an etching rate (nm/min).

(Method of measuring flatness)
A patterned substrate on which a copper wiring with a width of 180 nm was formed was immersed in the etching solution obtained in the Examples and Comparative Examples at 25°C for the time shown in Table 2 to etch the copper wiring. The substrate after etching was observed with an AFM (atomic force microscope) (model name "MFP-3D", manufactured by Oxford Instruments Ltd.), and the following calculations were performed.

The etching amount (nm) was calculated by determining the cross-sectional shape from the height data of the AFM image.
The root mean square height Sq (nm) was calculated by extracting only the wiring portion from the height data of the AFM image and using the following formula (1).
The maximum height - minimum height Sz (nm) was calculated by extracting only the wiring portion from the height data of the AFM image and using the following formula (2).
In the formula, A represents the reference area, and z represents the height at each measurement point (x, y).

(SEM observation)
A patterned substrate on which a 30 nm wide copper wiring was formed was immersed in the etching solutions obtained in the Examples and Comparative Examples at 25°C for the times shown in Table 2 to etch the copper wiring. The substrate after etching was observed with an FE-SEM (model name "S-4800", manufactured by Hitachi High-Technologies Corporation), and the shape of the copper wiring after etching was evaluated according to the following criteria.

A: No irregularities of 20 nm or more were observed.
B: Roughness of 20 nm or more was confirmed.

[Example 1]
The components were mixed so that the etching solution contained 0.11 mass% of component (A1) and the remainder of component (E1) in 100 mass% of the etching solution, to obtain an etching solution.
The evaluation results of the obtained etching solutions are shown in Table 2.

[Example 2]
The same procedure as in Example 1 was carried out to obtain etching solutions, except that the types and contents of raw materials were changed as shown in Table 1.
The evaluation results of the obtained etching solutions are shown in Table 2.

[Comparative Example 1]
The same procedure as in Example 1 was carried out to obtain etching solutions, except that the types and contents of raw materials were changed as shown in Table 1.
The evaluation results of the obtained etching solutions are shown in Table 2.

As can be seen from Table 2, the etching solution obtained in Comparative Example 1 left large irregularities after etching, whereas the etching solutions obtained in Examples 1 and 2 left small irregularities after etching, resulting in excellent flatness of the copper wiring after etching.

The etching solution and etching method of the present invention can be suitably used in the manufacture of semiconductor integrated circuits. They provide excellent flatness after etching and can etch fine structures in nanometer units. Therefore, they are preferably used in semiconductor integrated circuits in which wiring made of copper or copper alloys is present on the substrate surface, and are particularly suitable for semiconductor integrated circuits in which the wiring is present on the substrate surface at intervals of 100 nm or less.

Claims (10)

An etching solution for etching copper or copper alloys, comprising a chelating agent (A) containing at least one of aspartic acid and histidine , and substantially free of hydrogen peroxide. The etching solution according to claim 1, having a pH of 7 or higher. The etching solution according to claim 1 or 2, having a pH of 9 to 12. The etching solution according to any one of claims 1 to 3, further comprising a pH adjuster (B). The etching solution according to any one of claims 1 to 4, further comprising a surfactant (C). An etching method comprising the step of etching copper or a copper alloy using the etching solution according to any one of claims 1 to 5. The etching method described in claim 6, wherein wiring formed on a substrate surface from copper or a copper alloy is etched. The etching method of claim 7, wherein the spacing between the wiring lines is 100 nm or less. A method for manufacturing a semiconductor integrated circuit, comprising the step of etching copper or a copper alloy using the etching solution according to any one of claims 1 to 5. A method for manufacturing a semiconductor integrated circuit, comprising the etching method described in any one of claims 6 to 8.