Ruti Based Monolayer Films As Copper Interconnect Diffusion Barrier Layer Research

With the continuous shrinking of the minimum feature size in ultralarge-scale integration back-end technology, there is an urgent need for single-layer diffusion barrier in Copper interconnect. Due to the good adhesion between Ru and Cu, the Ru-based alloy has a potential of blocking the diffusion of Copper while keeping it adhesive. In this thesis, RuTi based alloy diffusion barrier, Ru-Ti, Ru-Ti-N, were investigated.The thermal stability of RuTa alloy was first studied as diffusion barriers for the purpose of reference. The experimental results show that the Ru-Ta alloy has a good barrier property to Cu. The SEM results show that with the increasing content of Ru, the agglomeration of Cu becomes severe after annealing.The Ru-N film fabricated under different Ar to N2 atmosphere was then investigated. Results show that the Ru-N film deposited with the ratio of Ar to N2 of 30:3 has the best thermal stability. But it is noticeable that a lot of pinholes showed on the surface of Cu after annealing at 400℃, which was the result of out-diffusion of N dissolved in Ru during PVD deposition, leading to the failure of the whole structure.Then RuTi and RuTiN films with different content of Ru:Ti were investigated as diffusion barrier to copper. For the RuTi film with very low Ti content, all three kinds of Ru-Ti films failed to block the diffusion of Cu after annealing at 500℃. With addition of N, the thermal stability of RuTiN barrier is improved. But a lot of pinholes can be observed on the SEM picture after annealing at 400℃, which suggests Ti of low content does not bind N and prevent the N-outdiffusion effectively.Furthermore, the barriers of Ru-Ti and Ru-Ti-N with higher content of Ti were fabricated. Thermal stability of Cu/barrier/Si and electrical characteristics of Cu/barrier/low k & SiO2 were studied. The results show that the Ru1Ti1N has the best thermal stability and no pinhole could be found on the surface of Cu after annealing. The electrical results also show that the Cu/RulTilN on the SiO2/Si and low k/Si has the best performance.Results of this thesis show that Ru1Ti1N has the best barrier property in all kinds of films we studied and has potential to be the competitor of Ru-Ta alloy diffusion barrier.