滴下水銀電極を用いる電気二重層微分容量の測定による銅電着の添加剤の吸着現象の解析

抄録

The adsorption behavior of addition agents used for electroplating of copper in acid copper sulfate bath was studied on a dropping mercury electrode relating to their concentration and electrode potential by measuring differential capacity of electrical double layer.
The potentials were measured by using Hg/Hg₂SO₄, 1N H₂SO₄ as a reference electrode. The zero charge potential of Hg electrode in 1N H₂SO₄ was estimated as zero volt for further discussion.
By the addition of thiourea (TU) or acetyl thiourea to 1N H₂SO₄, new peaks of capacity appeared at +0.6V and +0.75V.
When phenylthiourea was added to the same solution, the maximum of differential capacity at +0.15V appeared to decrease considerably.
These effects could be explained by the adsorption of TU and its derivatives on the surface of mercury electrode at rather positive potential.
Sodium β-naphthalene sulfonate (NS) and trisodium 1, 3, 5-naphthalene sulfonate had the similar effects on capacity-potential (C-E) curve, in which a minimum of differential capacity was observed at +0.3V and a maximum of that at -0.3V in the both agents. However, disodium 1, 5-naphthalene sulfonate gave a minimum at +0.3V and a maximum at 0V.
When TU and NS were concurrently added to 1N H₂SO₄, C-E curve was found as the sum of the each individual curve of each single addition agent. Therefore, it was concluded that there was no specific interaction between the adsorptions of TU and NS.
When benzotriazole was added to 1N H₂SO₄, the maximum at +0.15V in C-E curve remarkably decreased. By the addition of polyacrylamide, the differential capacity of electrical double layer noticeably increased at E>+0.55V and the maximum at +0.15V decreased.
It was found that methyl-isothiourea, glycine, and l-cystine had no effects on C-E curve in 1N H₂SO₄.