The phase formation and the morphological stability of ε1-Cu3Ge and ε1-Cu3(Si1−xGex) in Cu/epitaxial-Ge(e-Ge)/(111)Ge, Cu/(001)Ge, Cu/e-Ge/(111)Si, and Cu/(001)Si–Ge alloys have been investigated by transmission electron microscopy in conjunction with the energy dispersive spectrometry as well as by sheet resistance measurement. Epitaxial Cu and epitaxial ζ-Cu5Ge were found to form in as-deposited Cu/e-Ge/(111)Ge and Cu/e-Ge/(111)Si. On the other hand, textured Cu was found to form in the other systems. Polycrystalline ε1-Cu3Ge and ε1-Cu3(Si1−xGex) were the only phases formed in 150–500 °C annealed Cu/Ge and (Cu/e–Ge/Si and Cu/Si–Ge alloys) systems, respectively. They were found to agglomerate at 550 °C. The room-temperature oxidation of substrate in the presence of Cu3(Si1−xGex) was found only in the Cu/Si0.7Ge0.3 system. From the sheet resistance measurement, ε1-Cu3Ge has the lowest resistivity of 7 μΩ cm after 400 °C annealing. The electrical resistivity was found to decrease with the Ge content.