Microstructure and electrical resistivity of Cu and Cu₃Ge thin films on Si_1-xGe_x alloy layers

We have studied the reaction between Cu and Є₁-Cu₃Ge thin films and Si_1-xGe_x (x=0.5) alloy layers epitaxially grown on Si(100) in the temperature range of 250–400 °C. In this temperature range, Cu reacts with the alloy to form a Cu₃Si_1-xGe_x ternary phase with an ordered body-centered-cubic crystal structure, and no Ge segregation occurs during the reaction. Unlike Є₁-Cu₃Ge, the Cu₃Si_1-xGe_x films exhibit a high-room-temperature resistivity of ∼150 μΩ cm. However, the Cu₃Si_1-xGe_x phase is not observed when Ge is added to Cu to form Є₁-Cu₃Ge. In contrast to the results reported for films of Є₁-Cu₃Ge formed on Si(100) substrates, the outdiffusion of Si into the Є₁-Cu₃Ge films is found to be suppressed when the films are formed on Si_0.5Ge_0.5 layers at temperatures up to 500 °C, and their resistivity remains low (typically less than 10 μΩ cm at room temperature), indicating the increased stability of Є₁-C- u₃Ge on Si_1-xGe_x alloys. Furthermore, the Є₁-Cu₃Ge films form a sharp interface with the Si_0.5Ge_0.5 layers. These results indicate that Є₁-Cu₃Ge is an attractive candidate for contacts to SiGe-based devices. © 2000 American Institute of Physics.