FAILURE MECHANISMS OF TIN THIN-FILM DIFFUSION-BARRIERS

Reactively sputtered TiN has been studied for use as a diffusion barrier in the Al/TiN/Ti/Si metallization scheme in silicon-on-sapphire (SOS) integrated circuits. The diffusion barrier properties of TiN were found to depend critically on the concentration in the film. Two types of TiN thin films were studied in these experiments. Under no-bias condition, dark brown colored films (called B films) with low density (3.22 g cm-3), high electrical resistivity (about 400 μΩ cm) and 5-8% O2 were obtained. At -75 v dc substrate bias, bright golden colored films (called G films) with high density (about 5.0 g cm-3), low resistivity (about 20 μΩ cm) and negligible O2 were obtained. The G films were found to stop the silicon diffusion. But there was formation of intermetallics at the Al/TiN interface, which resulted in decomposition of the TiN film. The B films, though they were permeable to silicon, were found to stop this interaction. Based on the above results, a new metallization (Al/TiN(B)/TiN(G)/Si) was examined. RBS did not indicate any interactions after 2 h of annealing at 600°C. The film microstructure was studied by cross-sectional and planar TEM samples. These films were studied by RBS, AES, XRD and XPS to understand the diffusion and device failure mechanisms.