Control methods for the chemical-mechanical polishing process in shallow trench isolation

Process control of shallow trench isolation (STI) chemical-mechanical polishing (CMP) strongly relies on thickness measurements of various films. The control scheme based on send-ahead (SAHD) wafers with a fixed post-CMP target has low cost, but it neglects process variations before and during STI CMP. An "interactive" control method, based on extensive measurements, compensates for many of the variations in STI CMP, and eliminates the problem of underpolishing. However, this method comes with a high cost for multiple measurement steps. This paper compares fixed-target planarization to the interactive STI control methodology.