Sputtered TN was studied as a diffusion barrier in Cu/TiN/Ti/Si and Cu/TiN/Ti/SiO2/Si multilayer structures using various characterization methods, and their sensitivities for detecting breakdown of the barrier were compared. It was confirmed by scanning electron microscopy and Auger electron spectroscopy that breakdown of the TiN barrier occurred through out-diffusion of Si in addition to in-diffusion of Cu. Breakdown temperatures varied by more than 100 degrees C depending on characterization methods, and capacitance-voltage (C-V) measurement was most sensitive for detecting the failure of the TiN barrier. The effects of rapid thermal annealing (RTA) on barrier properties of TiN were investigated, and it was found by C-V measurement that the TiN(400 nm) RTA treated at 700 degrees C in a NH, ambient was stable up to 590 degrees C for 2 h, while the reference TiN (400 nm) was stable up to 450 degrees C for 2 h.