XPS investigations of thin tantalum films on a silicon surface

Ultra thin tantalum-based diffusion barriers are of great interest in copper metallisation technology. Even the smallest amounts of copper that diffuse into the active silicon regions on a microprocessor will alter their semiconducting properties thus leading to failure of the device. In the present work Ta films were deposited on silicon by electron beam evaporation and magnetron sputtering. The background of this study is investigation of interface formation, which is expected to have substantial influence on the properties of thin Ta films. All experiments were carried out under UHV conditions. This was necessary because Ta is a very reactive metal and is readily oxidized even at low oxygen partial pressure. The Ta4f peak, as a sensitive indicator of the chemical state, was analysed and compared to that for standard samples. Silicide formation is assumed to occur at the Ta/Si interface.