Due to the demand for a high throughput of through-silicon-vias (TSV) manufacture, fast via filling technique is required. Cu electrodeposition in methanesulfonic acid bath (MSA) is considered as one of the potential approaches to achieve the short time plating of TSV with larger diameter and deeper depth than the damascene via. In this paper, the effect of chloride ion in MSA plating bath on via filling for TSV was investigated by electron paramagnetic resonance and electrochemical techniques with a rotating disk electrode. Furthermore, wafer-segment plating using the real TSV structure is also examined. The results indicated that the chloride ions may form a "chloride bridge" to catalyze the reduction of Cu, and eliminate the inhibiting effect of PEG in MSA bath. Moreover, the Cl- accelerates the Cu deposition at the bottom of via where the electrochemical process is diffusion controlled, and inhibits the deposition at the top of via where that is non-diffusion controlled. These behaviors of chloride ion are very helpful to the TSV via filling. (C) 2013 The Electrochemical Society. [DOI: 10.114912.052304jes] All rights reserved.