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-annealin g 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 preferenti ally to the Cu. surface until a dense, uniform MgO layer of 150 Angstrom th ickness is formed. Substantial Mg segregation to the SiO2 or TiN surface al so takes place to form an interfacial MgO layer. Diffusion barrier characte ristics 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-alig ned surface MgO produced by the annealing process prevents interdiffusion o f 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 S iO2. Consequently, the thermal stability Of CU/SiO2/Si and Cu/TiN/Si multil ayer systems is significantly enhanced by introducing self-aligned surface and interfacial layers of MgO from Cu(Mg) alloy films.