Method of preparing electrolytic copper solution acidified with sulfuric acid, sulfuric-acid-acidified electrolytic copper solution prepared by the preparation method, and electrodeposited copper film
An object of the present invention is to provide a method for preparing a sulfuric acid base copper electrolytic solution used for formation of an electro-deposited copper film comprising a surface excellent in smoothness and gloss when formed by using the solution just after preparation and is prepared by using mono-sulfides. To achieve the object, a sulfuric acid base copper electrolytic solution is made to contain a sulfonated active sulfur compound, the bis(3-sulfopropyl)disulfide which is recommended for formation of a glossy electro-deposited copper film. And the bis(3-sulfopropyl)disulfide contained is obtained by converting a 3-mercapto-1-propanesulfonic acid into the bis(3-sulfopropyl)disulfide in an aqueous solution of the 3-mercapto-1-propanesulfonic acid by an oxidation reaction. In the oxidation reaction, an air bubbling method is preferably used to prevent oxidative decomposition of the 3-mercapto-1-propanesulfonic acid.
1. A method for preparing a sulfuric acid base copper electrolytic solution, comprising:
preparing an initial aqueous solution containing 3-mercapto-1-propanesulfonic acid at a concentration of 2.8×10 −6 mol/L to 2.3 mol/L and cupric ions, wherein the relationship between the concentration of the 3-mercapto-1-propanesulfonic acid and the concentration of the cupric ions in the initial aqueous solution satisfies the Expression 1:
[
Cupric
ion
concentration
(
mol
/
L
)
]
[
3
-
mercapto
-
1
-
propanesulfonic
acid
concentration
(
mol
/
L
)
]
≥
0.005
(
Expression
1
)
forming a cuprous salt of the 3-mercapto-1-propanesulfonic acid and the cupric ions as shown in the following Formula 1:
4MPS+2Cu 2+ →2Cu(I)S(CH 2 ) 3 SO 3 +SPS+4H + (Formula 1);
preparing a conversion solution by converting a part or all of the cuprous salt of the 3-mercapto-1-propanesulfonic acid into bis(3-sulfopropyl)disulfide by an oxidation reaction as shown in the following Formula 2:
2Cu(I)S(CH 2 ) 3 SO 3 +SPS+4H + +O 2 →2SPS+2H 2 O+2Cu 2+ (Formula 2)
using air in the initial aqueous solution in the presence of sulfuric acid; and
preparing a sulfuric acid base copper electrolytic solution by including the conversion solution in a copper sulfate-containing solution.
2. The method for preparing a sulfuric acid base copper electrolytic solution according to claim 1 , wherein the oxidation reaction is carried out at pH of 4 or less in the initial aqueous solution.
3. The method for preparing a sulfuric acid base copper electrolytic solution according to claim 1 , wherein the oxidation reaction using air comprises air bubbling.
4. The method for preparing a sulfuric acid base copper electrolytic solution according to claim 3 , wherein the air bubbling comprises a flow rate of supplied air of 0.1 L/min or more, and the relationship between total air volume supplied and the concentration of the 3-mercapto-1-propanesulfonic acid contained in the initial aqueous solution satisfies the Expression 2
[
Total
Air
Volume
(
L
)
]
[
Amount
of
3
-
mercapto
-
1
-
propanesulfonic
acid
in
initial
aqueous
solution
(
mol
)
]
≥
112
L
/
mol
.
Expression
2
5. The method for preparing a sulfuric acid base copper electrolytic solution according to claim 1 , wherein a concentration of copper ions in the copper sulfate-containing solution is 0.5 g/L to 100 g/L.
6. The method for preparing a sulfuric acid base copper electrolytic solution according to claim 1 , wherein the preparing an initial aqueous solution includes adding the 3-mercapto-1-propanesulfonic acid to an aqueous solution containing the cupric ions to form the initial aqueous solution.
7. The method for preparing a sulfuric acid base copper electrolytic solution according to claim 1 , further comprising including a quaternary ammonium salt polymer having a ring structure in the sulfuric acid base copper electrolytic solution.
8. The method for preparing a sulfuric acid base copper electrolytic solution according to claim 7 , wherein the concentration of the quaternary ammonium salt polymer having a ring structure is 1 ppm to 150 ppm.
9. The method for preparing a sulfuric acid base copper electrolytic solution according to claim 8 , wherein the quaternary ammonium salt polymer having a ring structure is a diallyldimethylammonium chloride polymer.
10. The method for preparing a sulfuric acid base copper electrolytic solution according to claim 1 , further comprising including chloride ion in the sulfuric acid base copper electrolytic solution, wherein the concentration of the chloride ion is 5 ppm to 100 ppm.
11. The method for preparing a sulfuric acid base copper electrolytic solution according to claim 1 , wherein the preparing a sulfuric acid base copper electrolytic solution by including the conversion solution in the copper sulfate-containing solution comprises adding the conversion solution to the copper sulfate-containing solution.