In this work we report an in situ transmission electron microscopy investigation of hole nucleation and growth under thermal processes. Two different systems are considered: a NiSi layer on poly-Si substrate without any interlayer and a NiSi+Mo (as metallic interlayer) system. This approach allows us to follow in situ hole formation and growth and to determine hole growth rate until the coalescence occurs. Furthermore, Rs measurements were performed for both systems to evaluate the effect of hole formation on electrical properties. The time and temperature dependences of the sheet resistance provide a relationship between the electrical properties and the morphological changes of the thin NiSi film during a thermal process. This dual characterization of nickel silicide with and without Mo ensures us on the key role of the interlayer in stabilizing the system when temperature is raised, causing a 60°C shift of the …