TiN/TiSi2 bilayers offering excellent stability as a barrier against Cu metallization have been made achievable through a two-step rapid thermal conversion process. TiN/TiSi2 bilayers are formed on single-crystalline Si substrates by the thermal conversion of Ti films in an ammonia ambient, using a rapid thermal process with a sequential two-step temperature cycle. In the thermal conversion process, the first-step is conducted in a low-temperature range, to minimize Ti/Si interaction, while maintaining reasonable interaction of Ti/NH3 and vigorous nitrogen diffusion through the Ti layer, to maximize the thickness of the TiN layer. Then, the second step is carried out at a relatively high temperature, to reduce Ti/Si interaction in the silicidation process. The TiN/TiSi2 bilayers show excellent diffusion barriers between Cu and single-crystal Si up to the annealing condition, 800 degrees C for 90 s; and the Cu film improve in quality by resulting from grain growth in a decrease of about 20% in sheet resistance. From the XRD results, only variation of peak intensities was observed due to grain growth of the Cu film for the 850 degrees C annealed samples. Also, there was no evidence of Cu diffusion through TiN for the 850 degrees C annealed samples on the Auger and RES results. It seems that enhanced barrier property of the Cu/TiN/TiSi2 stack is due to the thick TiN layer and the suppression of Ti-oxide formation by the low-temperature nitridation in the first step.