A method for monitoring the filling performance of a copper plating solution for microvia metallization was examined by a continuous operation in a pilot plating bath. The monitoring method was carried out using a simple galvanostat measurement. A potential difference between two polarization curves obtained from the galvanostatic measurements at different flow rates can serve as an effective indicator of filling performance, because a linear function can correlate the potential difference with the filling performance. The shift of the polarization curve of the working solution after a period of operation can be regarded as the occasion of accumulation of by-products. (c) 2006 The Electrochemical Society.