Phase formation was studied for Ni/Ti/Si and Ni/TiSi2 structures processed by vacuum RTP. Intermetallic compounds Ni3Ti and Ti2Ni form sequentially above 425 °C for metal bilayers Ni/Ti on Si, as Ni diffuses into Ti. When the temperature reaches 550 °C, Si becomes mobile and diffuses into the Ni–Ti compound, resulting in the growth of a ternary phase Ti4Ni4Si7, (V phase). If Ni is in excess with respect to this ternary silicide, a separate layer of Ni silicide grows between the substrate and the V phase, due to the fact that Ni is the main diffusing species. For the case of an excess Ti, the Si atoms are the most mobile species during Ti silicidation. Below 700 °C, TiSi2 grows with a C 49 structure whereas a mixture of TiSi2 C 54 and V phase forms at high temperature, without phase separation in distinct layers. Ni is also a fast diffuser in TiSi2. The activation energy for the diffusion along the grain boundaries of the Ti silicide is about 1.25 ± 0.2 eV. For these Ni/TiSi2 samples too, the same V phase starts to grow at the metal/silicide interface.