Formation of Cu$_6$Sn$_5$ intermetallic in Cu/Sn thin films

The study of the formation of the Cu$_6$Sn$_5$ intermetallic compound in Sn(55nm)/Cu(30nm) thin bilayer films was carried out directly in the column of a transmission electron microscope (electron diffraction mode) by heating the film sample from room temperature to 300$^\circ$C and recording the electron diffraction patterns. The thin films formed as a result of a solid state reaction were monophase and consisted of the $\eta$-Cu$_6$Sn$_5$ hexagonal phase. The temperature range for the formation of the $\eta$-Cu$_6$Sn$_5$ phase was determined. The estimate of the effective interdiffusion coefficient of the reaction suggests that the main mechanism for the formation of the Cu$_6$Sn$_5$ intermetallic is diffusion along the grain boundaries and dislocations.