US Patent 7101252 Polishing method and apparatus

A chemical mechanical polishing method for polishing an oxide film and a protective film formed on a substrate having recesses comprises four steps. The first step planarizes the oxide film using a polishing pad and a polishing agent containing cerium oxide particles by causing relative rotational motion between the substrate and the polishing pad. The second step continues polishing the oxide film to maintain the planarized property of the oxide film. The third step polishes the oxide film until at least a portion of the protective film becomes exposed. The fourth step polishes the oxide film until the oxide film is substantially removed and the protective film is substantially exposed. During the four steps, torque values are measured on the substrate or the polishing pad, and changes in torque with time are calculated. This information is used to determine the status of each of the steps during the polishing run.