In integrated-circuit (IC) industry, Cu is currently the most suitable material for interconnection in the metallization process because of its low resistivity and high melting point characteristics. However, high-temperature diffusion of Cu into Si and SiO2 causes severe damage to the device. A copper-silicon compound is formed at the interface, which greatly increases the resistivity. Therefore, a diffusion barrier must be deposited between the copper wire and the Si substrate or SiO2.

High entropy alloys(HEAs) are mostly comprised of transition metals. Transition metal nitride coatings are typically harder and more chemically inert compared to the metallic thin films, but they are often more brittle than the pure metals or alloys. Due to high mixing-entropies, the high entropy nitrides(HEANs) easily form solid solutions and due to large lattice-distortions caused by atoms of different sizes, effects such as inter-diffusion, growth, & nucleation, are all suppressed. Several HEANs have been demonstrated with extraordinary properties, such as high hardness, resistance to oxidation at high-temperatures, high corrosion resistance, high thermal stability and high structural stability. High temperature stability and suppressed diffusion suggests that HEANs may also be promising diffusion barriers.

Owing to the high resistance against inter-diffusion, high entropy alloys thin films have demonstrated great potential for diffusion barriers in copper/silicon interconnections in the integrated-circuit industry. In this paper, the novel (MoWCoNi)Nx high entropy nitrides thin films were designed based on a single-phase MoWCoNi and were fabricated by DC magnetron sputtering in a nitrogen atmosphere.

To evaluate its thermal stability, the Cu/(MoWCoNi)Nx/Si structure was rapidly thermally annealed(RTA) in high vacuum for different times to simulate the actual environment in the IC fabrication process. The layer maintains suitable thermal stability after RTA annealing for 5 minutes to 1 hour. No macropores or cracks were observed on the surface, and the layer remained amorphous without any grain boundaries and maintained good interfacial adhesion with Cu and Si. By increasing the nitride concentration, the conductivity decreased and the grain size also declined. The Cu/HENs/Si sandwiched structure showed better anti-diffusion characteristics than the Cu/TiN/Si at elevated temperatures.

The minimal amount of Cu that diffused into the layer suggested that inter-diffusion between the Cu and Si atoms was effectively suppressed. The excellent diffusion barrier performance and high temperature long-term thermal stability is attributed to the stable amorphous structure with no rapid diffusion path, and its structural and chemical stability. The diffusion kinetics were analyzed by depth-profiling X-ray photoelectron spectroscopy. The variation of the phase transition as a function of the nitrogen contents was analyzed by X-ray diffraction. As a result, the HENs become more diffusion resistant due to sluggish diffusion behaviors. Optimal engineering of the balance between resistivity and thermal stability of the (MoWCoNi)Nx HENs diffusion barrier was presented.