Characterization of Tungsten Carbide as Diffusion Barrier for Cu Metallization

Abstract

In this paper, the physical and electrical properties as well as thermal stability of the sputter-deposited tungsten carbide (WCx) film used as a diffusion barrier layer for copper metallization were investigated for the first time. It is found that the as-deposited WCx film has a nanocrystalline structure and a low electrical resistivity of approximately 227 µΩcm. According to the four-point probe technique, X-ray diffraction (XRD) and secondary ion mass spectroscopy (SIMS) measurements, it is found that WCx film can preserve the integrity of the Cu(2000 A)/WCx(600 A)/n-Si structure without the formation of Cu3Si up to 600°C annealing in N2 for 30 min. A more sensitive diode leakage current measurement of the Cu(2000 A)/WCx(600 A)/p+n-Si structure shows that WCx film is effective against Cu diffusion into Si substrate up to 550°C. The failure of WCx film in preventing Cu diffusion is attributed to the Cu diffusion into the Si substrate through local defects of the WCx barrier layer. It is found that Cu diffusion is strongly enhanced by the formation of W5Si3 at the WCx/Si interface after high-temperature annealing.