Evaluation of pad life in chemical mechanical polishing process using statistical metrology

Abstract

Statistical meirology was used to characterize the pad life in chemical mechanical polishing process. A special chip containing capacitor structures with dimensions laid out as per a fractional factorial design of experiment was used as a lest vehicle in this study. The wafer lot was separated into four splits and each split was polished at a different time depending on the wafer count since the last pad change in the chemical mechanical polishing system. Capacitance measurements were done on the test capacitors and the IMD thickness was determined from the 2D simulation of the capacitor. The wafer-level and die-level variations were determined using an application software program known as Variation Decomposition Analysis Program . The useful pad life can be determined by selecting the wafer count below which inter- and intra-die variations are allowable.