In this study, the critical dose for ion-beam mixing of Co and Si with Ge-ions which results in homogenous CoSi2 formation after rapid thermal annealing was found. For this purpose, Co was deposited by sputtering on chemically cleaned, <100>-oriented Si and subsequently mixed with Ge ions at doses in the range of 2. 1014 to 1. 1015 cm−2. Silicidation was performed in a rapid thermal annealing (RTA) system at temperatures between 700° and 100°C. Rutherford backscattering measurements showed that annealing at 700°C results in an incomplete reaction when ion-beam mixing at a dose of 2.1014 cm−2 or no ion-beam mixing was performed. After annealing at 1000°C, TEM samples revealed an inhomogeneous CoSi2 film consisting of large grains embedded in the Si. Mixing at doses at or above 5.1014 cm−2 and subsequent RTA at 700°C resulted in uniform CoSi2 layers. Higher annealing temperatures cause larger grains and resistivity values as low as 18 μΩcm. Therefore, we demonstrated that the critical dose leading to complete formation of smooth CoSi2 films with abrupt interface is 5.1014 cm−2 which is nearly the same value as the amorphization dose of Ge in Si.