Comparison of WTi and WTi(N) as diffusion barriers for Al and Cu metallization on Si with respect to thermal stability and diffusion behavior of Ti

• We compare the effectivity of WTi and WTi(N) as diffusion barriers for aluminum and copper.
• WTi works better for Cu than for Al whereas WTi(N) improves the performance for both.
• We show that Ti diffusion out of WTi into Al and Cu can affect the barrier stability.
• Ti diffusion can be depressed by nitrogen incorporation.
• We focus on the effects of varying the annealing time.

The thermal stability of WTi and WTi(N) as diffusion barriers for Al and Cu metallization on Si (1 0 0) was investigated by time of flight secondary ion mass spectrometry (ToF-SIMS) depth profiling, X-ray diffraction (XRD), electron microscopy (SEM and TEM) and X-ray photoelectron spectroscopy (XPS). For both, Al and Cu, Ti diffusion out of WTi into the metal was proved to occur at elevated temperatures (400 °C for Al and 600 °C for Cu) which further results in barrier film failure. Nitrogen incorporation into WTi leads to an elimination of the Ti diffusion and consequently to a better thermal stability of the barrier film. It is shown that besides crystal structure, Ti diffusion into the metallization is an essential factor of the barrier failure mechanism. The failure temperature for Al is lower than for Cu.