The interdiffusion of Ni from fully silicided NiSi metal gates through gate dielectrics into the Si substrate after N-2 annealing or forming gas annealing consistent with back-end-of-line thermal budgets is presented by using back-side secondary ion mass spectrometry profiling. Ni penetration is observed through 1.3 nm thick SiON into the Si channel region after annealing for 60 min at temperatures of 350 - 400 degrees C. However, Ni penetration through 1.5 nm HfSiON/0.8 nm SiO2 film into the Si channel is close to the limit of detection after annealing under similar conditions. The results suggest that Ni penetration can be suppressed by a dielectric film with sufficient thickness. (c) 2006 The Electrochemical Society.