Properties of reactively sputtered WNx as Cu diffusion barrier

Abstract

Reactively sputtered WNx thin films have been studied as a diffusion barrier between Cu and Si. By changing the ratio of N2 to Ar+N2 gas flow rate at a total pressure of 5mTorr with RF power of 200W, WNx films with seven different compositions were deposited. Amorphous WNx structure was obtained for the films below 32% nitrogen content, and polycrystalline W2N structure above that. After annealing of Si/WNx/Cu samples in 10% H2/Ar forming gas ambient for 1h, X-ray diffraction, scanning electron microscopy, Auger electron spectroscopy and sheet resistance measurements were employed to characterize barrier performance. Amorphous WNx with thickness of 100nm maintained its barrier property up to 800°C, while poly-W2N failed at temperature lower than 800°C because of the release of excess nitrogen. Even though the thickness of WNx barrier was reduced to 5nm, amorphous WNx films maintained the Si/WNx/Cu structure up to 600°C for 1h. Among the amorphous WNx films, W68N32 was the most stable composition for various thicknesses.