Effect of thickness scaling on the permeability and thermal stability of Ta(N) diffusion barrier

Abstract

Molecular and atomic permeability, thermal stability and interfacial reactions of ultrathin Ta, TaN and Ta/TaN stack as barrier to Cu/low - k interconnects have been studied. It is shown the barrier layers containing TaN and Ta/TaN have good thermal stability and barrier properties when their thickness is >3.5 nm while Ta cannot withstand 450 °C annealing. The thinner barriers are permeable for neutral molecules like heptane and demonstrate degradation of resistivity during the thermal anneal at 450 °C. Penetration of Ta precursors into low-k and formation of TaO/TaC type of bonds increase the dielectric function of low-k dielectric. Our results show that, on the low-k material with 23% porosity and 0.9 nm pore radius, the PVD deposited Ta(N) films <3.5 nm thick have poor barrier function and are sufficient for neutral molecules penetration, especially water molecules.