Diffusion barrier properties of TiN films for submicron silicon bipolar technologies

Abstract

We have studied the properties of reactively sputtered TiN films used as diffusion barriers for Al-Cu metallization in submicron bipolar transistors. Emitter-base diodes with shallow junctions were fabricated to monitor the integrity of the barrier via junction leakage measurements. Scanning and transmission electron microscopy were used to study the morphology and step coverage of these films, and also for barrier failure analysis. The effectiveness of the barrier depends on both the nominal thickness of the TiN layer and on the device dimensions. For thin TiN layers (∼47 nm), high junction leakage was observed on narrow emitters (0.5 μm) but not on wide emitters (5 μm). These observations highlight the reliability and yield concerns associated with the use of sputtered TiN films for deep submicron technologies. In some cases, low-temperature (500°C) epitaxial alignment of the emitter polysilicon was observed, associated with Al penetration of the barrier. This indicates that the Al provides an enhancement of the tendency towards epitaxial alignment of the polysilicon grains. For thicker TiN layers (∼83 nm), low leakage was observed on both narrow and wide emitters, and no unusual epitaxial alignment was observed.