Preparation And Characterization Of Barrierless Cu (Sn), Cu (C),Cu(Sn,C) Films

Owing to the decrease of interconnect feature size with the development of the integrated circuits, a successful thin barrier layer with good thermal stability is often difficult to be achieved. A barrierless scheme is proposed using a Cu-based materials added with various elements or substances. In this paper, barrierless Cu(Sn), Cu(C) and Cu(Sn,C) films were deposited on Si(100) substrates by RF magnetron sputtering technique. The microstructure and properties of sputtered Cu films with various elements, such as individual large atom element Sn, individual small atom element C, simultaneous Sn and C, were studied.Sn has a small solid solubility in Cu and reacts easily with Cu to form compounds. Cu films doped with different concentrations of Sn were prepared with the purpose of researching diffusion-hindering mechanism of this kind of atom in Cu films. The results showed that electrical resistivities decreased with the drop of Sn content. Differernt Sn compositions having various situations in Cu films induced diversity of diffusion-hindering effects. The Cu-Sn compounds were detected in Cu films doped with Sn contents exceeding the solid solubility. Cu consumed solid solution Sn, so the diffusion-hindering effect was not primely displayed. The results confirmed that the lower resistivity and higher stability of Cu films can be achieved by the strict control of the doping concentrations and the existing state of Sn element (solid solution without compounds and precipitates).Cu (4.6 at.% C) and Cu (4.7 at.% C) films were also discussed. Adding small atom C in the Cu films can obtain a lower resistivity. Meanwhile, C atom was effective in inhibiting grain growth during annealing and played an important role of improving the thermal stability of the film. In addition, C was prone to diffuse to Cu(C)/Si interface. A stable SiC layer was formed on the top of Si substrate in Cu(4.7 at.% C) film with a more carbon content, but this phenomenon was not observed in Cu(4.6 at.% C) film.This layer hindered efficiently the interdiffusion of Cu and Si, leading to a greater extent enhancement of thermal stability. So Cu-Si compounds were not found in the Cu (4.7 at.% C) films after annealing at 400℃for 40h. The results showed that the diffusion-hindering effect was influenced by differernt concentrations of C in Cu films.The resistivity value of ternary Cu (0.6 at.% Sn,2 at.% C) film codoped with large atom Sn and small atom C was smaller than that of binary Cu (0.6 at.% Sn) film, and the Cu-Si compounds were found in the two films after annealing at 700℃for 1h. The results showed that they had almost the same themal stability. Furthermore, since the Cu film was doped with C and Sn, a nanoscale self-passivation amorphous layer was formed in the Cu(Sn,C)/Si interface after annealing at 700℃for 1h. This layer was different from native oxide layer and inhibited availably the Cu-Si interdiffusion. Accordingly, simultaneously adding Sn and C in the Cu film can obtain a lower resistivity and enhance the thermal stability of the film. But the Cu-Si compounds were discovered in the Cu(0.6 at.% Sn,2 at.% C) and Cu(0.6 at.% Sn) films annealed at 600℃for 5h and the resistivity increased dramatically. The results indicated that the thermal stability of the two films for a long time was poor.