US Patent 7718536 Planarization process for pre-damascene structure including metal hard mask

A planarization process for a pre-damascene structure is described, wherein the pre-damascene structure includes a metal hard mask that is disposed on a first material layer with a damascene opening therein and a second material layer that fills the damascene opening and covers the metal hard mask. A first CMP step is conducted using a first slurry to remove the second material layer outside the damascene opening. A second CMP step is conducted using a second slurry to remove the metal hard mask.