Root cause identification in yield degradation due to nickel-silicide disconnection

This paper describes the yield degradation caused by nickel silicide (NiSi) disconnection in a salicide formation process used in system on chip (SoC) manufacturing. Physical analysis revealed that the failure was caused by a NiSi disconnection on a gate electrode. To identify the root cause in such a complicated issue, “Semimetrics,” which integrates a statistical analysis and the equipment data of many variables (e.g., EES data), are useful and clarified that the root cause of the failure is the residence time of a wafer in the rinse tank. However, as is common knowledge, NiSi does not dissolve in pure water in a rinse tank, since it is regarded as a safety tank free of acid. To comprehend Semimetrics result, the physical model is suggested. Through the validation of the physical model, we found that acid exists in the rinse tank and that acid contamination leads to NiSi dissolving. Consequently, univariate FDC using a residence time could completely prevent the failure due to the NiSi disconnection without incurring additional cost.