In-situ transmission electron microscopy study of thermal stability and carbide formation in amorphous Cu-Mn/C films for interconnect applications

In this study, the thermal stability and Mn carbide formation were investigated in amorphous Cu-Mn/C films with potential applications as interconnect layers. Amorphous Cu-Mn films (with 50 and 70 at% Mn content) were deposited by direct current (DC) magnetron sputtering at room temperature. Evaporated carbon foils were used as substrates to model low-κ carbon doped oxides in their reaction with Cu-Mn films. In-situ transmission electron microscopy indicated that the amorphous state was stable below 300 °C, where the films crystallized into Cu(Mn) and α-Mn based solid solutions. The Mn carbide phases appeared at 400 °C where it was accompanied by the disappearance of the α-Mn phase and a decrease in the Mn content of the Cu(Mn) phase. The Mn23C6 and Mn5C2 carbide phases were present from 400 °C to 500 °C, and Mn5C2 and Mn7C3 carbides in the temperature range of 500-600 °C. The Mn5C2 carbides exhibited significant grain growth in the temperature range of 400-600 °C. The activation energies for Mn5C2 growth were 101 ± 20 and 88 ± 22 kJ/mol in the films containing 50 and 70 at% Mn, respectively, thereby indicating that growth was facilitated by a higher Mn content. In addition to carbide formation, surface oxidation occurred in the system. Thermodynamic considerations indicate that Mn carbide formation can only occur in the Cu-Mn-C-O system when the Mn is not fully oxidized and free metallic Mn atoms remain.