The ring oscillator is an important tool for inline monitoring during technology development, as it contains the most important front end of line technology features, is testable at first metal, and generally shows a good correlation to SRAM yield. This work explores various failure analysis techniques for the ring oscillator, during the development of 14 nm FinFET technology. OBIRCH, which is typically a DC technique, was operated with voltages as low as 0.15 V to find multiple defect mechanisms affecting the yield of ring oscillators, which operate at a frequencies in the GHz range. In contrast to typical photon emission analysis of ring oscillators, examines the devices which are flipping on, it is here proposed that the OBIRCH spots which are generated are indications of the Ioff, or the leakage of devices in the inverter stages across the ring. The results from this failure analysis approach enabled a rapid improvement in yield not only of the ring oscillator itself but of the SRAM.

Test structure characterization plays a predominant role throughout the entire development cycle of a product. They are used to understand the process windows and also help to monitor the health of line (HOL). One of the key principles in successfully monitoring the HOL is to establish passing and failing electrical criteria to various test structures. This paper shows electrical and physical characterization of one such test structure. Further, a novel way of establishing electrical signatures to specific defect fail mode finger prints for early identification and monitoring of process-related defects is proposed.