Patent Application
20230025950
The present invention relates to a copper electroplating solution comprising sulfuric acid and a compound having a specific structure, a method of producing the copper electroplating solution, and to a copper electroplating method comprising using the copper electroplating solution.
In the formation of a fine wiring, a through silicon via (TSV), and a bump in a highly integrated electronic circuit, an approach involving filling a metal in a pattern, such as a groove or a hole, has heretofore been used. Copper electroplating is one typical approach involving filling a metal. Of such approaches, copper electroplating involving filling copper as a metal has been widely used. In the formation of a circuit by the copper electroplating, it is required that a copper layer having a high purity and satisfactory surface flatness be formed in order to obtain high connection reliability.
As a copper electroplating solution that has heretofore been known, for example, in Patent Literature 1, there is a disclosure of a copper plating bath containing 0.8 M copper sulfate and 0.5 M isethionic acid. In addition, in Patent Literature 2, there is a disclosure of a copper plating bath containing copper oxide and isethionic acid, and in Patent Literature 3, there is a disclosure of a copper plating bath containing copper sulfate pentahydrate, sulfuric acid, hydrochloric acid, and a trace amount of isethionic acid.
However, when copper electroplating is performed with each of the copper electroplating solutions as described in Patent Literatures 1 to 3 above, there have been problems in that a copper layer excellent in surface flatness cannot be obtained, and further, a copper layer to be obtained has a low purity. Accordingly, an object of the present invention is to provide a copper electroplating solution capable of providing a copper layer that has a high purity and is excellent in surface flatness.
The inventors of the present invention made investigations, and as a result, found that the above-mentioned object can be achieved by using a copper electroplating solution comprising a sulfate ion, a copper ion, and a compound having a specific structure at predetermined blending ratios. Thus, the inventors completed the present invention.
That is, according to one embodiment of the present invention, there is provided a copper electroplating solution, comprising the following components: (A) a sulfate ion; (B) a compound represented by the following general formula (1); and (C) a copper ion, wherein the copper electroplating solution has a content of the component (B) of from 0.3 part by mass to 50 parts by mass and a content of the component (C) of from 5 parts by mass to 50 parts by mass with respect to 100 parts by mass of a content of the component (A):
where R1 and R2 each independently represent a hydrogen atom, a sodium atom, a potassium atom, or an alkyl group having 1 to 5 carbon atoms, and “n” represents 1 or 2.
In addition, according to one embodiment of the present invention, there is provided a copper electroplating method comprising using the above-mentioned copper electroplating solution.
According to the copper electroplating solution of the present invention, the copper layer that has a high purity and is excellent in surface flatness can be obtained.
Embodiments of the present invention are described in detail below.
<Copper Electroplating Solution>
A copper electroplating solution of the present invention is a copper electroplating solution containing, as essential components, the following components: (A) a sulfate ion (hereinafter also referred to as “component (A)”); (B) a compound represented by the general formula (1) (hereinafter also referred to as “component (B)”); and (C) a copper ion (hereinafter also referred to as “component (C)”).
A supply source for the component (A) (sulfate ion) is not particularly limited, but for example, at least one kind selected from the group consisting of: sulfuric acid; copper sulfate; iron sulfate; lead sulfate; silver sulfate; calcium sulfate; potassium sulfate; sodium sulfate; barium sulfate; magnesium sulfate; aluminum sulfate; nickel sulfate; a mixture thereof; and a hydrate thereof may be used. Those supply sources for the component (A) may be used alone or in combination thereof. The supply source for the component (A) to be used is preferably at least one kind of sulfuric acid, copper sulfate, or copper sulfate pentahydrate, more preferably a combination of sulfuric acid and copper sulfate or copper sulfate pentahydrate because a copper layer that has a higher purity and is excellent in surface flatness can be obtained.
The component (B) is a compound represented by the following general formula (1):
where R1 and R2 each independently represent a hydrogen atom, a sodium atom, a potassium atom, or an alkyl group having 1 to 5 carbon atoms, and “n” represents 1 or 2.
In the general formula (1), R1 and R2 each independently represent a hydrogen atom, a sodium atom, a potassium atom, or an alkyl group having 1 to 5 carbon atoms. Examples of the alkyl group having 1 to 5 carbon atoms represented by each of R1 and R2 may include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a secondary butyl group, a tertiary butyl group, a pentyl group, and a neopentyl group. R1 preferably represents a hydrogen atom or a sodium atom, and more preferably represents a hydrogen atom because a copper layer that is more excellent in surface flatness can be obtained. R2 preferably represents a hydrogen atom.
In the general formula (1), “n” represents 1 or 2. “n” preferably represents 2 because a copper layer that is more excellent in surface flatness can be obtained.
Preferred specific examples of the compound represented by the general formula (1) include the following compounds No. 1 to No. 12. In the following compounds, the symbol “Me” represents a methyl group, the symbol “Et” represents an ethyl group, and the symbol “iPr” represents an isopropyl group.
Of the above-mentioned compounds, the compounds No. 2, No. 7, and No. 8 are preferred, and the compound No. 7 is more preferred.
A supply source for the component (C) (copper ion) is not particularly limited, but for example, at least one kind selected from the group consisting of: copper sulfate; copper chloride; copper bromide; copper hydroxide; a mixture thereof; and a hydrate thereof may be used. Those supply sources for the component (C) may be used alone or in combination thereof. The supply source for the component (C) to be used is preferably copper sulfate or copper sulfate pentahydrate because a copper layer that has a higher purity and is excellent in surface flatness can be obtained.
The content of the component (B) in the copper electroplating solution is from 0.3 part by mass to 50 parts by mass with respect to 100 parts by mass of the content of the component (A). The content of the component (B) is preferably from 1 part by mass to 30 parts by mass, more preferably from 3 parts by mass to 20 parts by mass with respect to 100 parts by mass of the content of the component (A) because a copper layer that is more excellent in surface flatness can be obtained.
The content of the component (C) in the copper electroplating solution is from 5 parts by mass to 50 parts by mass with respect to 100 parts by mass of the content of the component (A). The content of the component (C) is preferably from 10 parts by mass to 40 parts by mass, more preferably from 20 parts by mass to 30 parts by mass with respect to 100 parts by mass of the content of the component (A) because a copper layer that has a higher purity and is excellent in surface flatness can be obtained. The content of the component (B) is preferably from 1 part by mass to 200 parts by mass, more preferably from 5 parts by mass to 100 parts by mass, most preferably from 10 parts by mass to 70 parts by mass with respect to 100 parts by mass of the content of the component (C) because a copper layer that has a higher purity and is excellent in surface flatness can be obtained.
The concentration of the component (A) (sulfate ion) in the copper electroplating solution is not particularly limited, but is generally from 10 g/L to 500 g/L, preferably from 50 g/L to 350 g/L, more preferably from 100 g/L to 250 g/L, still more preferably from 110 g/L to 200 g/L.
The concentration of the component (B) in the copper electroplating solution is not particularly limited, but is generally from 0.3 g/L to 80 g/L, preferably from 1 g/L to 60 g/L, more preferably from 5 g/L to 40 g/L, still more preferably from 5 g/L to 35 g/L.
The concentration of the component (C) in the copper electroplating solution is not particularly limited, but is generally from 5 g/L to 250 g/L, preferably from 10 g/L to 150 g/L, more preferably from 20 g/L to 80 g/L, still more preferably from 25 g/L to 70 g/L.
The copper electroplating solution of the present invention may contain, as a component except the above-mentioned component (A) to component (C), a chloride ion source, a plating promoter, a plating inhibitor, or the like
The chloride ion source is not particularly limited, but examples thereof include hydrogen chloride and sodium chloride. The concentration of the chloride ion source in the copper electroplating solution is preferably from 5 mg/L to 200 mg/L, more preferably from 20 mg/L to 150 mg/L.
The plating promoter is not particularly limited, but examples thereof include compounds represented by the following general formulae (2) to (4).
XO3S—R—SH (2)
XO3—Ar—S—S—Ar—SO3X (3)
In the general formulae (2) and (3), R represents a substituted or unsubstituted alkyl group, preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms, Ar represents a substituted or unsubstituted aryl group, such as a substituted or unsubstituted phenyl group or naphthyl group, and X represents a counterion, such as a sodium or potassium ion.
In the general formula (4), R21 and R22 each represent a hydrogen atom, a linear or branched alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 5 to 9 carbon atoms that may have a substituent having 1 to 3 carbon atoms, or an aryl group that may have a substituent having 1 to 3 carbon atoms, M represents an alkali metal, ammonium, or a monovalent organic ammonium, and “n” represents a number of from 1 to 7.
Of those described above, sodium 3,3′-dithiobis(1-propanesulfonate) (hereinafter sometimes abbreviated as “SPS”) is preferred as the plating promoter from the viewpoint that SPS has a high promoting effect on the formation of a copper layer.
The concentration of such plating promoter in the copper electroplating solution is preferably from 0.1 mg/L to 100 mg/L, more preferably from 0.5 mg/L to 50 mg/L, most preferably from 1 mg/L to 30 mg/L.
For example, an oxygen atom-containing high-molecular weight organic compound may be used as the plating inhibitor. Specific examples thereof include polyethylene glycol, polypropylene glycol, a polyoxyethylene-polyoxypropylene random copolymer, and a polyoxyethylene-polyoxypropylene block copolymer. Of those, polyethylene glycol is preferred. From the viewpoint of further improving the effect of the present invention, the molecular weight of such oxygen atom-containing high-molecular weight organic compound is preferably from 500 to 100,000, more preferably from 1,000 to 10,000. In particular, polyethylene glycol having a molecular weight of from 1,000 to 10,000 is most preferred. From the same viewpoint, the concentration of the oxygen atom-containing high-molecular weight organic compound in the copper electroplating solution is preferably from 50 mg/L to 5,000 mg/L, more preferably from 100 mg/L to 3,000 mg/L.
In the present invention, a well-known solvent may be used as a solvent for the copper electroplating solution. Examples of the solvent include: water; alcohols, such as methanol, ethanol, isopropyl alcohol, and n-butanol; acetic acid esters, such as ethyl acetate, butyl acetate, and methoxyethyl acetate; ethers, such as tetrahydrofuran, tetrahydropyran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, dibutyl ether, and dioxane; ketones, such as methyl butyl ketone, methyl isobutyl ketone, ethyl butyl ketone, dipropyl ketone, diisobutyl ketone, methyl amyl ketone, cyclohexanone, and methylcyclohexanone; and hydrocarbons, such as hexane, cyclohexane, methylcyclohexane, dimethylcyclohexane, ethylcyclohexane, heptane, octane, toluene, and xylene. Those solvents may be used alone or in combination thereof.
Of those solvents, water and alcohols are preferred, and water is more preferred.
Any other additive known to be capable of being added to a plating solution may be optionally used in the copper electroplating solution of the present invention to the extent that the effect of the present invention is not inhibited.
Examples of the other additive include an anthraquinone derivative, a cationic surfactant, a nonionic surfactant, an anionic surfactant, an amphoteric surfactant, an alkanesulfonic acid, an alkanesulfonic acid salt, an alkanesulfonic acid ester, a hydroxyalkanesulfonic acid ester, and a hydroxyalkanesulfonic acid organic acid ester (provided that a compound corresponding to the component (B) of the present invention is excluded). The concentration of such other additive in the copper electroplating solution is preferably from 0.1 mg/L to 500 mg/L, more preferably from 0.5 mg/L to 100 mg/L.
The pH of the copper electroplating solution is not particularly limited, but generally acidic conditions of pH 4 or less, preferably acidic conditions of pH 3 or less, and more preferably strong acidic conditions of pH 2 or less are adopted. For the measurement of the pH, a pH meter LAQUA F-70 manufactured by HORIBA, Ltd. or the like may be used. A temperature at the time of the measurement of the pH may be about room temperature.
<Copper Electroplating Method>
Next, a copper electroplating method comprising using the copper electroplating solution of the present invention is described. The copper electroplating method of the present invention may be performed in the same manner as a related-art copper electroplating method except that the copper electroplating solution of the present invention is used as a copper electroplating solution. Herein, a copper electroplating method comprising forming a copper layer on a substrate to be plated is described.
For example, a paddle stirring-type plating apparatus only needs to be used as a copper electroplating apparatus. The plating tank of the copper electroplating apparatus is filled with the copper electroplating solution of the present invention, and the substrate to be plated is immersed in the copper electroplating solution. For example, a product obtained by forming a resist pattern on a Si substrate with a copper seed layer through use of a photoresist may be used as the substrate to be plated.
At this time, for example, the temperature of the copper electroplating solution is from 10° C. to 70° C., preferably from 20° C. to 60° C., and a current density falls within the range of from 1 A/dm2 to 70 A/dm2, preferably from 5 A/dm2 to 50 A/dm2, more preferably from 15 A/dm2 to 35 A/dm2. In addition, for example, air stirring, quick liquid current stirring, or mechanical stirring with a stirring blade or the like may be used as a method of stirring the copper electroplating solution.
When copper is filled in an opening portion of the resist pattern under such conditions as described above, a copper layer that has a high purity and is excellent in surface flatness can be formed on the substrate to be plated.
A plated product to be manufactured by using the copper electroplating method of the present invention is not particularly limited, and examples thereof include a wide range of products, such as materials for automobile industry (such as a heat sink, a carburetor part, a fuel injector, a cylinder, various valves, and an inner part of an engine), materials for electronic industry (such as contact, a circuit, a semiconductor package, a printed board, a film resistor, a capacitor, a hard disk, a magnetic material, a lead frame, a nut, a magnet, a resistor, a stem, a computer part, an electronic part, a laser oscillation device, an optical memory device, an optical fiber, a filter, a thermistor, a heater, a heater for high temperature, a varistor, a magnetic head, various sensors (gas, temperature, humidity, light, speed, and the like), and MEMS), precision instruments (such as a copying machine part, an optical instrument part, and a timepiece part), aviation or ship materials (such as an instrument of a hydraulic system, a screw, an engine, and a turbine), materials for chemical industry (such as a ball, a gate, a plug, and a check), various dies, a machine tool part, and a vacuum apparatus part. The copper electroplating method of the present invention is preferably used for the materials for electronic industry, in which a particularly fine pattern is required, is more preferably used in the manufacture of, among the materials, a semiconductor package and a printed board typified by TSV formation, bump formation, and the like, and is most preferably used in the semiconductor package.
Now, the present invention is described in more detail by way of the Examples and the Comparative Examples. However, the present invention is by no means limited by the following Examples and the like.
Sulfuric acid, the component (B), copper sulfate pentahydrate, hydrochloric acid, SPS, PEG4000, and water were mixed so as to give compositions shown in Table 1 to obtain Example copper plating solutions 1 to 9. The balance in each of the compositions of the copper plating solutions shown in Table 1 was water, and the concentration of each component was adjusted with water. In addition, SPS (manufactured by Tokyo Chemical Industry Co., Ltd.) and PEG4000 (manufactured by ADEKA Corporation) used in the Examples are disodium 3,3′-dithiobis(1-propanesulfonate) and polyethylene glycol having a weight-average molecular weight of from 3,600 to 4,400, respectively.
Plating baths of Examples and Comparative Examples shown in Tables 1 and 2 below all had a pH of from 0 to 1.
Sulfuric acid, the component (B) or another component, copper sulfate pentahydrate, hydrochloric acid, SPS, PEG4000, and water were mixed so as to give compositions shown in Table 2 to obtain Comparative copper plating solutions 1 to 8. The balance in each of the compositions of the copper plating solutions shown in Table 2 was water, and the concentration of each component was adjusted with water. In addition, SPS and PEG4000 used in Comparative Examples are disodium 3,3′-dithiobis(1-propanesulfonate) and polyethylene glycol having a weight-average molecular weight of from 3,600 to 4,400, respectively. Comparative compounds 1 to 5 used as the other components are compounds shown below.
A paddle stirring-type plating apparatus was used as a copper electroplating apparatus, and the plating tank of the paddle stirring-type plating apparatus was filled with each of the copper electroplating solutions of Examples 1 to 9 and Comparative Examples 1 to 8. A substrate to be plated was immersed in each of the copper electroplating solutions. A product obtained by forming a resist pattern (shape: having an opening portion of a circular sectional shape, opening diameter: 75 μm) on a Si substrate with a copper seed layer through use of a photoresist was used as the substrate to be plated. Next, copper of each copper electroplating solution was filled in the opening portion of the resist under the following plating conditions by a copper electroplating method. Thus, a copper layer was formed on the substrate to be plated.
(Plating Conditions)
(1) Hole diameter: 75 μm
(2) Current density: 18 A/dm2
(3) Liquid temperature: 35° C.
(4) Plating time: A time period required for the minimum level (LMin) of a copper layer to become 40 μm
A minimum level 3 (LMin) and a maximum level 4 (LMax) of a copper layer 1 formed on the surface of a substrate 2 to be plated by each of Evaluation Examples 1 to 9 and Comparative Evaluation Examples 1 to 8 as illustrated in
ΔL=LMAX−LMIN
In Table 3, a smaller value of ΔL means that a copper layer that was more excellent in surface flatness was able to be formed. In addition, a smaller value of the “Organic residue” means that a copper layer that had a higher purity was able to be formed. It was found from the results of Table 3 that in each of Evaluation Examples 1 to 9, a copper layer, which had a small content of the organic residues and was excellent in surface flatness as compared to those of Comparative Evaluation Examples 1 to 7, was able to be formed. In particular, it was found that in each of Evaluation Examples 1 and 2, a copper layer that was particularly excellent in surface flatness was able to be formed. In Comparative Evaluation Example 8, the organic residues were not detected, but the value of LL was large, and a copper layer that was excellent in surface flatness could not be formed.
As described above, it was found that when a copper layer was formed on the substrate to be plated by the copper electroplating method comprising using the copper electroplating solution of the present invention, a copper layer that had a high purity and was excellent in surface flatness was able to be formed.
1 copper layer, 2 substrate to be plated, 3 minimum level (LMIN), 4 maximum level (LMAX), 5 ΔL.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-219370 | Dec 2019 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/043577 | 11/24/2020 | WO |
