Effect of nitrogen content on the degradation mechanisms of thin Ta–Si–N diffusion barriers for Cu metallization

The effect of the nitrogen content on the thermal stability and degradation mechanisms of Ta–Si–N diffusion barriers was studied using methods that prove Cu interdiffusion. On the one hand, glancing angle X-ray diffraction was applied to detect Cu3Si formation after annealing of Cu/Ta–Si–N/Si layer stacks. On the other hand, a combined secondary ion mass spectroscopy and transmission electron microscopy analysis of Ta–Si–N/Cu/Ta–Si–N/SiO2/Si samples was performed. For a detailed investigation of the microstructure evolution, the crystallization behavior of both Cu-capped and uncapped Ta–Si–N/Si samples was analyzed using X-ray diffraction. In the case of an uncapped Ta73Si27 film, Si interdiffusion from the substrate precedes the layer crystallization. The substrate influence on the crystallization process decreases with increasing N content xN of the Ta–Si–N layer. Using Cu/Ta–Si–N/Si samples, a critical temperature for Cu silicide formation was determined. This temperature increases with increasing N content of the Ta–Si–N barrier. In the case of Ta–Si–N films with xN > 25 at.%, Cu interdiffusion into the substrate occurs before a significant barrier crystallization is observed. For Ta–Si–N layers with xN ≤ 25 at.%, no indications for Cu diffusion before crystalline phase formation were detected.