This study investigates the formation of Ni silicides on Si1-y C y (0≤y≤0.02) epilayers grown on Si(001). The presence of C atoms retards the growth kinetics of NiSi and significantly enhances the thermal stability of NiSi thin films. In particular, an abnormal redistribution of C atoms in the NiSi thin films was observed during Ni silicidation. The NiSi layer was split into two sublayers by an obvious pileup of C atoms. This study proposes a mechanism to elucidate this phenomenon in terms of the C solubility. C atoms accumulated at the NiSi/ Si1-y Cy interfaces and NiSi grain boundaries may act as diffusion barriers, effectively hindering the grain growth and agglomeration of NiSi and extending the process window of low resistivity NiSi silicides.