Preparation Of Tantalum Silicon Nitride Diffusion Barrier Layer Integrated Circuit Copper Interconnect And Barrier Characteristics

With the development of integrated circuit (IC) and increase in the degree of integration, the feature size is shrinking and traditional Al metallization cannot satisfy the requirement of electrical device. To reduce the interconnection delay, Cu metallization is taking the place of traditional Al interconnection due to its lower resistivity and superior resistance to electromigration. However, adhesion of Cu to Si substrate is poor. In addition, Cu atoms are quite mobile and can diffuse into Si easily, leading to formation of Cu-Si compounds. Cu atoms act as deep level impurities, affecting the reliability of devices. Therefore, it is inevitable to add diffusion barrier between Si and Cu.On the basis of a comparative study of the diffusion barriers on their fabrication methods and characteristics, Ta-Si-N thin films and Cu/Ta-Si-N thin films were deposited on p-type Si(111) substrates by dual-targets magnetron reactive sputtering. Then rapid thermal annealing (RTA) was performed on the samples. The sheet resistance, surface morphology, crystalline structures and chemical composition of the films were characterized by four-point probe (FPP) sheet resistance measurement, atomic force microscopy (AFM), scanning electron microscope (SEM), X-ray diffraction method (XRD) and energy disperse spectroscopy (EDS), respectively.The experiment shows that when doped with Si and N, the barrier property of Ta-based thin films is improved. When doped with Si, the crystallization of Ta nitrides can be suppressed effectively. And when Si content gets higher, the degree of amorphism is increased. The as-deposited Ta-Si thin-film is nano-crystalline. When doped with N, the as-deposited thin-film becomes amorphous which means the N addition can suppress the crystallization of Ta silicides effectively. The diffusion barrier property of Ta-Si-N has much to do with Si sputtering power and N₂/(N₂+Ar). When the N₂/(N₂+Ar) flow rate is fixed, there is an optimal value of the Si target sputtering power and it can make the Ta-Si-N barrier possess the best barrier property and the barrier performance is degraded when Si content is too high or too low. And the diffusion barrier property of Ta-Si-N barrier is improved with the N₂/(N₂+Ar) increasing, but not evidently when N content beyond 50%.The failure of the barriers is mainly attributed to the Cu diffusion. Cu atoms diffuse through grain boundaries of the barriers or diffuse the amorphous structure of Ta-Si-N layers directly, and react with Si to form the Cu₃Si phase.The crystallization temperature of Ta-Si-N thin films is high and the interfacial stability of Cu/Ta-Si-N/Si structures is good. Also, the adhension of Cu with Ta-Si-N is strong, and no Cu film falling is observed.