We report an oxalic acid (OA)-based, nonalkaline slurry for chemical mechanical planarization (CMP) of interconnect structures containing Cu/Ta over mechanically and chemically fragile, low-k dielectrics. This slurry uses a single dispersion (a pH-controlled mixture of OA, hydrogen peroxide, and fumed silica) to remove both Cu lines and Ta barrier by simply varying the operating pH. Chemically promoted Ta removal is achieved at nearly pH-independent rates between pH 3.0 and 6.0. Cu planarization can be pH-tuned to remove bulk Cu at high rates at pH 3.0 and residual Cu at lower rates (to minimize dishing) at pH 5.0-6.0. (c) 2008 The Electrochemical Society.