Phase formation in Cu(Sn) alloy thin films

Abstract

The interdiffusion of Cu and Sn and the formation and dissolution of Cu-Sn precipitate phases have been examined for Cu(Sn) alloy thin films. Cu(Sn) films were deposited by electron beam evaporation in either a Sn/Cu bilayer or Cu/Sn/Cu trilayer film structure, with overall Sn concentrations from 0.1 to 5 atomic percent. Analysis by in situ resistivity, calorimetry, electron diffraction and x-ray diffraction measurements indicates that the bilayer and trilayer films form the intermetallic phase η-Cu6Sn5 during film deposition. Upon heating, the ε-Cu3Sn phase forms at 170 °C, then this phase dissolves into the Cu matrix at approximately 350 °C. Finally, ζ-Cu10Sn3 phase forms and precipitates after heating to 500 °C and cooling to room temperature. The final resistivity of Cu/Sn/Cu films with more than 2 atomic percent Sn was greater than 3.5 μΩ-cm. However, resistivities from 1.9 to 2.5 μΩ-cm after annealing were obtained with Cu/Sn/Cu films containing less than 2 atomic percent Sn.