The impact of V-th-adjusting layers on high-k/metal-gate n- and pFinFET V-th stability is investigated. Additional insight is gained by monitoring Delta V-th recovery transients over several decades in time. V-th-adjusting capping layers deposited directly on top of the gate dielectric degrade the V-th stability. The V-th stability improves as the capping layers are buried in the gate metal and are thus isolated from the gate dielectric. A combination of a capping layer thickness and depth in the metal gate is found that practically eliminates nFET V-th instability. (C) 2009 American Vacuum Society. [DOI: 10.1116/1.3054352]