The physical properties and thermal stability of sputter-deposited WCx films were investigated for the first time. It was found that as-deposited WCx films had a nanocrystalline structure and a low electrical resistivity. Four-point probe techniques, X-ray diffraction and secondary ion mass spectroscopy measurements showed that WCx films could preserve the integrity of a Cu(200nm)/WCx(60nm)/n-Si structure, without the formation of Cu3Si, during 600C annealing in N2 for 0.5h. More sensitive diode leakage-current measurement of a Cu(200nm)/WCx(60nm)/p+n-Si structure showed that WCx films were effective, against Cu diffusion into Si substrates, at up to 550C. The failure of WCx film in preventing Cu diffusion was attributed to Cu diffusion into the Si substrate via local defects in the WCx barrier layer. It was found that Cu diffusion was strongly enhanced by the formation of W5Si3 at the WCx/Si interface after high-temperature annealing.

Characterization of Tungsten Carbide as a Diffusion Barrier for Cu Metallization. S.J.Wang, H.Y.Tsai, S.C.Sun: Japanese Journal of Applied Physics - 1, 2001, 40[4B], 2642-9