Electrolytic copper process using anion permeable barrier

Processes and systems for electrolytically processing a microfeature workpiece with a first processing fluid and an anode are described. Microfeature workpieces are electrolytically processed using a first processing fluid, an anode, a second processing fluid, and an anion permeable barrier layer. The anion permeable barrier layer separates the first processing fluid from the second processing fluid while allowing certain anionic species to transfer between the two fluids. The described processes produce deposits over repeated plating cycles that exhibit resistivity values within desired ranges.