Analysis of Cu(I) in copper sulfate electroplating solution was conducted by absorption of a chelate of Cu(I) with bathocuproinedisulfonic acid, disodium salt (BCS). Although the absorption of new copper sulfate electroplating solutions was negligible, the absorption of operating solutions was clear. The difference of new solutions and operating solutions was also verified using an electrochemical method for detection of Cu(I). We concluded that the Cu(I) ions are measurable using this chelate reagent. The absorption increased quickly in a few minutes after mixing with the chelate reagent and subsequently continued to increase slowly. To clarify this phenomenon, the organic compounds in the plating solutions were analyzed and Cu(I)-PEG (polyethylene glycol) complexes with different chain lengths were detected using MALDI-MS. Results show that Cu(I) ions exist in the plating solutions not only as small complexes with small organic compounds but also as large complexes with PEG. Small complexes of Cu(I) can react quickly with BCS and cause the rapid increase of the absorption in a few minutes after mixing. Cu(I)-PEG complexes prevent the chelating reaction of Cu(I) with BCS by steric hindrance of PEG, which explains the subsequent slow increase of the absorption. Using this chelate method, we monitored quantities of Cu(I) in copper sulfate electroplating production lines, detected the variation of Cu(I) quantities, and found the increase during the resting state of the lines.

Analysis of Cu(I) in copper sulfate electroplating solutions was conducted by absorption of a chelate of Cu(I) with bathocuproinedisulfonic acid, disodium salt (BCS). The absorbance of the color reaction of Cu(I) increased quickly in a few minutes after mixing with the chelate reagent and subsequently continued to increase slowly. To analyze the reaction kinetics of the color reaction, we divided Cu(I) complexes into two groups, small complexes and large Cu(I)-PEG complexes, and assumed the reaction of each group of complexes and BCS is a first order reaction with a specific reaction rate constant. We simulated the absorption curve with a good correlation and obtained the concentrations and the time constants, inverse of rate constants, of small complexes and large Cu(I)-PEG complexes. These concentrations and time constants are important parameters to control plating solutions. The time constant of small complexes can be attributed to the variation of the proportions of these small complexes. The smaller time constant of Cu(I)-PEG complexes can be considered the larger size distribution of Cu(I)-PEG with different chain lengths. Using this analysis, we monitored the variation of Cu(I) concentration in production lines for one month and found the increase of small complexes during the resting state of the lines. This increase corresponded to the tendency of occurring of brightening troubles.

In this study, we investigated a behavior of cuprous ion (denoted as Cu(I)) in the copper sulfate plating solution and effects of the Cu(I) on a quality of Cu plating film. Through spectroscopic method, two kinds of holding structure of Cu(I) in the plating solution were firstly indicated by analyzing the kinetics of complex forming reaction between the Cu (I) and bathocuproinedisulfonic acid, disodium salt (BCS). One component is ignited from Cu(I) probably incorporated into deep inside of polyethylene glycol (PEG), and the Cu(I) must have steric hindrance of PEG to be interacted with the BCS in plating solution. Another one is a component for Cu(I) which can be instantaneously reacts to the BCS to be complex. In addition, interestingly, it has been shown that instantaneous component is affecting the roughness of Cu plating film. These results indicate that spectroscopic measurement and analysis is effective for the management and evaluation of the plating solution for high quality production.

Formation and accumulation of Cu(I) in copper sulfate electroplating solutions were discussed. By electrolysis, the accumulation of Cu(I) in the plating solutions was also confirmed in the laboratory. Accumulation rate and amount will depends on the current density and electrolysis time and the dissolved gases. Cu(I) is held in an aqueous solution as a complex with PEG, and gradually it is consumed by oxidation or disproportionation reaction. In the plating solutions using a nano bubble water, formation and accumulation rate of Cu(I) was different by gas species dissolved. Our results indicate the possibility for control of Cu(I) in the plating solutions.

Bathocuproinedisulfonic acid, disodium salt (BCS) is generally used to detect Cu(I) through a color reaction. We newly found BCS fluorescence in the visible blue region in an aqueous solution. However, the fluorescence mechanism of BCS is not well known, so we should investigate its fundamental information. We confirmed that the characteristics of fluorescence are highly dependent on the molecular concentration and solvent properties. In particular, owing to the presence of the copper compound, the fluorescence intensity extremely decreases. By fluorescence quenching, we observed that a copper compound concentration of 10 %6 mol/L or less could easily be measured in an aqueous solution. We also observed BCS fluorescence in copper sulfate plating solution and the possibility of detecting monovalent copper by fluorescence reabsorption.