Influence of incorporated non-metallic impurities on electromigration in copper damascene interconnect lines

Low electromigration in Cu interconnect lines represents one of the major challenges for a good performance of semiconductor devices. Referring to this, experiments were carried out to study the influence of non-metallic impurities like Cl, S, and C incorporated in Cu during the electrochemical deposition. In the case of a lower impurity content a higher resistance against electromigration was verified. The electromigration activation energy for metallizations with small contaminations was found to be (1.00 ± 0.06) eV whereas Cu interconnect lines with high non-metallic impurities revealed an activation energy of (0.65 ± 0.03) eV. The electromigration induced degradation by void formation starts at the top interface between Cu and dielectric cap layer. Probably, this results from high mechanical stresses due to differences in material properties or due to an interface weakening by the segregation of S and C impurities.     

Diffusion barrier performances of thin Mo, Mo-N and Mo/Mo-N films between Cu and Si

In this work, we have studied the diffusion barrier performances of Mo, Mo-N and Mo/Mo-N metallization layers deposited by sputtering Mo in Ar/N₂ atmospheres, respectively. Samples were subsequently annealed at different temperatures ranging from 400 to 800 °C in vacuum condition. The film properties and their suitability as diffusion barriers and protective coatings in silicon devices were characterized using four-point probe measurement, X-ray diffractometry, scanning electron microscopy, Auger electron spectroscopy and transmission electron microscopy analyses. Experimental results revealed that the Mo (20 nm)/Mo-N (30 nm) layer was able to prevent the diffusion reaction between Cu and Si substrate after being annealed at 600 °C for 30 min. The adhesion between layers and the content of N atoms are the key parameters to improve the properties of Mo-based barrier materials. The Mo layer interposed between Cu and Mo-N diluted the high nitrogen concentration of the barrier and so enhanced the barrier performances.