Transmission electron microscopy studies of brown and golden titanium nitride thin films as diffusion barriers in very large scale integrated circuits

Abstract

The usefulness of reactively sputtered TiN as a diffusion barrier in the AlTiN/Ti/Si metallization scheme in very large scale integration was reported in a previous publication. Two types of TiN thin films were studied in these experiments. Depending on the applied substrate bias voltage, the resulting TiN films can have different properties. Under no-bias conditions, dark brown colored films (called B films) with low density (3.22 g/cm3), high electrical resistivity (∼400 μΩ cm), and 5%–8% O2 are obtained. A+ -75 V dc substrate bias, bright golden colored films (called G films) with high density (∼5.0 g/cm3), low resistivity (∼20 μΩ cm), and negligible O2 are obtained. Even though the B films contain more O2, the G films were found to be better diffusion barriers for silicon. To investigate the effect of film microstructure on the diffusion barriers, cross-sectional and planar transmission electron microscopy samples were used. Both, brown and golden, types of films have columnar grain structure with approximately the same size (∼400–500 Å), contrary to fine-grained structure observed for G films by some other groups. The columns in the G films increase in size with an increase in distance from the TiN/Si interface, while the grain size remains almost constant in the B films. The intergrain structure also differs considerably; the grains in G films are very closely packed while they are very loosely bound in the B films. The intergrain voids in the B films can act as an easy path for silicon diffusion. Also, these films were studied by Rutherford backscattering spectroscopy, Auger electron spectroscopy, and x-ray diffraction to understand the diffusion mechanisms.