Resistivity and diffusion barrier properties of ZrN in Cu/ZrN/Si system

摘要

Ever since copper replaces alumina, one of the most serious problems has been that copper diffuses fast in silicon and then reacts with Si to form high resistive Cu-2Si compound, leading degradations of the integrated circuits (ICs). In order to successfully integrate Cu metallization into ICs, a diffusion barrier preventing the interdiffusion or reaction between Cu and the adjoining material is necessary. In general, the potential diffusion barriers demand high conductivity, good adhesion, high thermal stability, chemically inert with copper and silicon, low resistivity and lacking of grain boundaries. Transition metals and nitrides are extensively investigated as barrier materials due to their good thermal stability and electrical properties in Cu metallization. The nitride compound series includes HfN. WN, TiN, TaN. and Ta-Si-N and these layers prevented the Cu diffusion only at temperatures below 600 deg C. However, process temperature as high as 700deg C is sometimes required, a more promising diffusion barrier is needed. On the other hand, ZrN possesses the relatively large heat of formation, DELTAH=-87.3 kcal/mol, compared with DELTAH = -80.4 kcal/mol and DELTA H = -60.3 kcal/mol for TiN and TaN, respectively. ZrN as a good barrier in Al/ZrN/Si has also been reported. Therefore, ZrN represents an interesting material of better candidate for the diffusion barrier. In this study, we deposited ZrN by magnetron sputtering on Si(001) substrates to investigate the thickness dependence of electrical resistivity. Then we study the diffusion behaviour of the constituent species in Cu/ZrN/Si stacks during annealing. Finally the diffusion coefficient and activation energy of Cu in the ZrN barrier were determined with various ZrN thickness. Micro structure is used to explain the enhanced barrier properties of the thick ZrN films.