Ruthenium Cobalt to Extend the Scalability of Ultra-thin Direct Plate Liners

In traditional semiconductor technology a sputtered copper seed layer is used to improve the adhesion, microstucture, and electromigration characteristics of electrochemically deposited (ECD) copper. The seed layer is deposited on top of a Ta/TaN stack. The Ta layer acts as an adhesion and nucleation layer for the copper seed and the TaN serves as a diffusion barrier for the Cu. As the line widths continue to shrink, scaling each of these layers becomes more difficult. It would be advantageous for the interconnect to be composed of as much copper as possible, transitioning from the traditional liner seed stack to a single layer that could function as a diffusion barrier, adhesion promoter, and a directly plateable surface could improve the extendibility of copper interconnect technology.;Novel mixed phase films grown by plasma-enhanced atomic layer deposition (PEALD) have been investigated as direct-plate Cu barriers for advanced back end of the line integration. Previous work on RuTaN mixed phase materials has shown that a Ru:Ta ratio of 12:1 has been effective as a direct plate Cu barrier to a thickness of 2-3 nm based on the resistivity of the film. To try and scale direct plate barrier technology below 2 nm the resistivity of the films needs to be decreased. To accomplish this, the use of Co in place of traditional barrier materials is proposed as an alternative approach.;RuCo liner films with metal ratios between 5:1 and 15:1 were investigated as both a direct plate surface and for their ability to act as a robust Cu diffusion barrier. 3 nm thick PEALD RuCo films with a metal ratio between 5:1 and 15:1 exhibited plating characteristics comparable to a PEALD Ru film. The RuCo films were also demonstrated to be a suitably robust Cu diffusion barrier. The scalability limits of the RuCo film are limited by the resistivity of the film. When the thickness of the film was reduced to 2 nm the resistivity of the film increased to a point that the electrochemical deposition of Cu became non-uniform. The RuCo films were also found to be structurally unstable when the thickness of the films was increased to 6 nm. This resulted in the phase transition within the RuCo film which caused an order of magnitude increase in the Cu diffusion measured through the RuCo films. The direct-plateable PEALD RuCo films appear to be scalable to a thickness of 2 nm and may offer an alternative route for the continued scaling of Cu interconnects.