Energetic ion-based deposition and implantation of metal-nitride diffusion barriers for microelectronics applications by plasma source ion implantation

The research involves the study of process development and materials science issues in the synthesis and deposition of metal nitride diffusion barrier films for microelectronics applications. The films were deposited using the plasma source ion implantation (PSII) process in the energetic ion assisted deposition (EIAD) and in the ion implantation modes. Initial work was performed on TiN and Cu multilayer films deposited on Si substrates using the PSII system modified with rotatable and retractable sputter cathodes. These modifications made the system cluster-compatible and permitted multiple modes of operation in a sequential manner without breaking vacuum. The system was subsequently used for more detailed studies on the deposition of Cu diffusion barrier films of Ta and TaN_x. Electron microscopy showed the films to consist of grains tens of nanometers in size with grain boundary widths in the range of 1–4nm. Both, increasing the nitrogen content of the feed gas and pulse biasing of the substrate stage resulted in grain size reduction. Grazing incidence x-ray diffraction showed the presence of a metastable cubic TaN phase in the TaN_x films. Nitrogen ion implantation of the films was performed at 20 kV with doses ranging from 1 to 4 × 1017 ions/cm2. For Ta films implantation resulted in the formation of the equilibrium Ta₂N phase, and for the TaN_x films it led to supersaturation of the metastable TaN phase as evidenced by lattice parameter expansion. Isochronal annealing of the films at temperatures ranging from 500 to 750°C followed by Auger analysis and sheet resistance measurements showed the films to be effective diffusion barriers. Nitrogen ion implantation of the pre-deposited EIAD films was shown to dramatically improve diffusion barrier properties due to stuffing of the grain boundaries with nitrogen that impedes diffusion. Best results were observed for Ta and TaN_x films implanted with nitrogen at intermediate doses, where the implanted Ta was effective at preventing interdiffusion up to at least 750°C. The relative contribution of grains and the grain boundaries to the overall diffusivity was determined by applying the Whipple model to experimentally determined Auger data.