The thermal stability of Cu/FSG structure with amorphous and crystalline tantalum nitride diffusion barriers

This work investigates the thermal interactions of Cu/Ta-N/Ta/fluorinated silicate glass (FSG) structures after annealing up to 900°C, where Ta-N layers are as-deposited amorphous TaN_x (x∼0.5) or polycrystalline TaN films. It is found that both TaN, and TaN barriers possess excellent capability to prevent Cu from diffusing after annealing at 700°C or lower. After annealing at 800°C, however, inward diffusion of Cu occurred in Cu/Ta-N/FSG structures. The outward diffusion of fluorine was also observed. After annealing at 900°C, reaction spots, which exposed the underlying FSG layer, were observed on the surface and formation of oxide phases was detected in the Cu/TaN_x/FSG structure. However, exposure of FSG and oxidation were not found in the Cu/TaN/FSG structure. Nevertheless, in Cu/TaN/FSG structure, the sheet resistance was found to increase drastically after annealing at 900°C. The significant increase in the sheet resistance could be attributed to the agglomeration of Cu. The influences of TaN_x and TaN interlayers on the thermal stability of Cu/FSG system are discussed on the basis of chemical composition of these two Ta-N barriers.