Potential of low-resistivity Cu2Mg for highly scaled interconnects and its challenges

Materials with low resistivity in small dimensions are urgently desired to replace Cu for highly scaled interconnection in advanced integrated circuits. This study reports the possibility of Cu2Mg intermetallic compound as a Cu alternative by showing adequate adhesion on SiO2, a low resistivity of 25.5 μΩcm at 5 nm film thickness and good trench-filling capability in trench width of 38 or 23 nm by sputtering reflow. However, annealing at 400 °C for 30 min led to the dielectric current leakage associated with the formation of a thick MgO layer. Furthermore, Mg composition inside the trenches was less than the stoichiometric Cu2Mg composition. Theoretical calculation of surface diffusion process revealed that the adatom hopping of Mg atoms was slower than that of Cu atoms, which resulted in the Mg-poor composition inside the trenches.