A method for performing an electrochemical plating (ECP) process includes contacting a surface of a substrate with a plating solution comprising ions of a metal to be deposited, electroplating the metal on the surface of the substrate, in situ monitoring a plating current flowing through the plating solution between an anode and the substrate immersed in the plating solution as the ECP process continues, and adjusting a composition of the plating solution in response to the plating current being below a critical plating current such that voids formed in a subset of conductive lines having a highest line-end density among a plurality of conductive lines for a metallization layer over the substrate are prevented.