3-Mercapto-1-Propanesulfonate for Cu Electrodeposition Studied by in Situ Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy, Density Functional Theory Calculations, and Cyclic Voltammetry

Abstract

We investigate the mechanism of 3-mercapto-1-propanesulfonate (MPS) acceleration of Cu electrodeposition in the presence of Cl– through comparison with the inactive but related model compounds 1-butanesulfonate and 1-butanethiol (BuSH). In situ shell-isolated nanoparticle-enhanced Raman spectroscopy was used to evaluate these additives as a function of potential. MPS adsorbs to the Cu electrode in the presence of Cl– through the thiol functional group. Density functional theory calculations reveal that the adsorption of thiol has a depolarizing effect on the strength of the interaction between adsorbed Cl– and the electrode surface, the consequences of which are observed spectroscopically. The sulfonate moiety does not interact directly with the electrode. However, cyclic voltammetry used to assess the permeability of adsorbed MPS and BuSH adlayers indicates that the sulfonate group has a more direct role in Cu deposition beyond simple disruption of the surface layer.

Cuprous Ion Mass Transport Limitations During Copper Electrodeposition

“…This concentration was well in the range of cuprous ion concentrations, which would be estimated at such cupric ion concentration using equilibrium constants reported in the literature (vide infra). Determination of the cupric ion concentration via the same method but at overpotentials of approximately −500 mV (compare Figure a) using the corresponding diffusion coefficient ( D =5.37×10 −6 cm 2 s −1 ) yielded [Cu 2+ ]=0.151±0.008 M, which is in very good accordance with the theoretical value ([Cu 2+ ]=0.157 M).…”

“…Another possible explanation could be related to different surface coverages of sulfate or chloride at different rotational speeds and corresponding different catalytic activities for copper deposition. Sulfate was found to adsorb onto copper surfaces in the absence of chloride . Residual trace amounts of chloride might originate from copper sulfate and sulfuric acid.…”

Effects of Temperature on the Comproportionation of Metallic Copper and Cupric Ions to Cuprous Ions

“…This behavior was ascribed to either transport phenomena of smallest residual amounts of dissolved oxygen or different sulfate surface coverages at different rotational speeds and corresponding different catalytic activities for copper deposition. Sulfate was found to adsorb onto copper surfaces in the absence of chloride . The potential regime exhibiting such counterintuitive behavior was found to increase with decreasing temperature.…”

Effects of Brighteners in a Copper Plating Bath on Throwing Power and Thermal Reliability of Plated Through Holes

“…[26,27] Because MPS has a thiol group, it can strongly adsorb on copper surface and enhance copper deposition rate. [26,[28][29][30][31] As to UPS and ZPS, both have no thiol group but a thiouronium group and a benzothiazolyl group, respectively. Although both molecules still have the MPS moiety, their adsorption ability is totally different from that of MPS.…”