Thermal stability enhancement of Cu interconnects by employing a self-aligned MgO layer obtained from a Cu(Mg) alloy film

Self-aligned surface and interfacial M-O layers were formed by pre-annealing CU(Mg)/Si0(2)/Si and Cu(Mg)/TiN/Si multilayer films at 500 degreesC in an oxygen ambient, resulting in the structures Of MgO/CU/MgO/SiO2/Si and MgO/Cu/MgO/TiN/Si, respectively. During pre-annealing, Mg segregates preferentially to the Cu. surface until a dense, uniform MgO layer of 150 Angstrom thickness is formed. Substantial Mg segregation to the SiO2 or TiN surface also takes place to form an interfacial MgO layer. Diffusion barrier characteristics of the surface MgO layer were investigated by vacuum-annealing the Si/MgO/CU(Mg)/MgO/SiO2/Si multilayer structure. It was shown that self-aligned surface MgO produced by the annealing process prevents interdiffusion of Cu and Si up to 700 degreesC. Furthermore, interfacial MgO between Cu and SiO2 or TiN reduces diffusion of Cu into the Si substrate at temperatures up to 700-800 degreesC, indicating that self-aligned interfacial MgO plays an important role in suppressing interdiffusion between the Cu and TiN or SiO2. Consequently, the thermal stability Of CU/SiO2/Si and Cu/TiN/Si multilayer systems is significantly enhanced by introducing self-aligned surface and interfacial layers of MgO from Cu(Mg) alloy films.