STABILITY OF TIB2 AS A DIFFUSION BARRIER ON SILICON

The stability of low-pressure chemical vapor-deposited TiB2 films has been investigated for their potenital use as diffusion barriers between Al or Cu metallurgy and the Si substrate during post-metal annealing at temperatures ranging from 450-640-degrees-C for Al, and 500-800-degrees-C for Cu. Although no evidence of intermixing was observed via Rutherford backscattering spectroscopy (RBS) for TiB2/Si samples rapid thermal-annealing (RTA) up to 1080-degrees-C, pyramid-shape pits in the Si, bounded by (111) planes, were observed using transmission electron microscopy for the samples annealed above 950-degrees-C. Secondary ion mass spectroscopy depth profiles of B in Si originating from the TiB2 solid source suggested enhanced diffusion after RTA. According to RBS spectra coupled with scanning electron microscopy (SEM) examination, Al/TiB2/Si (pre-annealed) stacks appeared to be stable up to 500-degrees-C for 30 min in forming gas. For the stacks with as-deposited (amorphous) TiB2 films, plan-view SEM of Al/TiB2/Si showed very limited reaction with Al up to 600-degrees-C, in good agreement with sheet resistance measurements. The as-deposited, amorphous TiB2 films were superior diffusion barriers compared to the annealed, polycrystalline TiB2. No interaction took place between sputtered Cu and an underlying, amorphous TiB2 film up to 750-degrees-C, 30 min in vacuum. Plan-view SEM, RBS, and sheet resistance measurements showed that the structure started to break down at 775-degrees-C.