Effective FA Approach in Uncovering Gate-to-D/S Tungsten Spur Fabrication Defect

Abstract A series of power supply line controller failures at Analog Devices Incorporated (ADI) exhibited abnormal output voltage and quiescent current symptoms. Our failure analysis revealed a gate-to-drain/source tungsten spur defect, which required a sophisticated multi-step detection process. The investigation combined several advanced techniques: light emission microscopy (LEM) and optical beam induced resistance change (OBIRCH) identified the failing circuit, passive voltage contrast (PVC) located the affected transistor, and nanoprobing with electron beam induced resistance change (EBIRCh) pinpointed the gate-to-source/drain leakage location. Focused ion beam (FIB) cross-sectioning proved crucial for physical analysis, as conventional chemical deprocessing would have destroyed the tungsten spur and potentially misidentified the defect as electro-static discharge damage. Transmission electron microscopy confirmed the spur's composition as tungsten, and subsequent fabrication investigation traced the root cause to a titanium nitride barrier breach at the contact bottom, occurring where contacts intersect with spacer nitride. The issue was resolved through critical dimension tightening at the fabrication site.