IMPROVEMENT OF DIFFUSION BARRIER PROPERTIES OF RF-SPUTTERED MOLYBDENUM

In a contact metallization employing Mo as a thin-film ″diffusion barrier″ , the authors have observed that this refractory metal does not exhibit optimum barrier properties when rf sputtered in argon. It was found that the use of similar 1500 A of rf-sputtered Mo between Si and Au results in extensive Si and Au intermixing in less than 30 min at 450 degree C. Auger depth profile analysis confirmed that both Si and Au had moved through the Mo. This would preclude subsequent processing involving elevated temperature, as in a Silox deposition. The intermixing appears to proceed via a grain boundary diffusion mechanism (E//a equals 0. 21 eV). Significant improvement in the intermixing time was obtained by the controlled incorporation of N//2 into the Mo via reactive rf sputtering. A possible model for this improvement will be presented using the data obtained from microstructural analysis of the nitrided and unnitrided films.