Sn was selected as an alloying element of Cu. The Cu-Sn thin layers were deposited on the Si substrates by the electroplating method and their properties were studied. By rapidly thermal annealing(RTA) up to 40$0^{circ}C$ after electroplating, sheet resistance decreased and adhesion strength increased, but that trend was reversed at the 50$0^{circ}C$ RTA. Cu-Sn particles grew dense and the surface was uniform up to 40$0^{circ}C$, but at 50$0^{circ}C$, empty area was introduced and the surface became rough owing to oxidation and particle coarsening and agglomeration. Deposited layer contained significant amount of Si, while pure Cu-Sn layer with the composition ratio of 90:10 was present only on the top surface. However, no significant change in the Cu composition within alloy layers occured by the RTA regardless of its temperature. This indicates that the Cu diffusion into the Si was suppressed by the presence of Sn.