We report on the room-temperature synthesis of the low-resistivity TaSi2 phase using ion-beam mixing of Ta/Si bilayers with Ar ions. The formation of the silicide phase is observed for different damage energies deposited at the Ta/Si interface. The variance Δσ2 of the reacted (TaSi2) layer thickness varies linearly with the ion fluence Φ and the reaction rate Δσ2/Φ is proportional to the deposited damage energy density FD. The measured mixing/reaction efficiency, Δσ2/ΦFD = 10 ± 1 nm5/keV, is in agreement with the value calculated by the model of compound formation under local thermal spikes.