Composition and thermal stability of ultrathin tantalum oxide films on Si and TiN/Si substrates

As dimensions of ULSI devices continue to shrink at a phenomenal pace, novel (high-K) dielectrics will be required for deep sub-micron high-performance logic and memory devices. Ta_2O₅ films (with a dielectric constant of about an order of magnitude higher than that of SiO_2) is one of the candidates to replace conventional SiO₂ dielectrics. The focus of our work is to understand the composition of ultrathin (less than 10 nm) tantalum oxide films deposited on Si(100) and TiN(100 nm)/Si(100) substrates and to explore the evolution of these films upon thermal processing. High resolution medium energy ion scattering has been used for depth profiling of Ta, O, Si, and N in the films. In the case of a Si(100) substrate, we observed an intermediate SiO_x layer between tantalum oxide and the silicon substrate, also seen by cross-sectional TEM. The thickness of this layer is estimated to be about 2 nm, increasing to 3 nm after annealing in vacuum at 900^oC. In the case of the TiN substrate, the interface between the deposited dielectric and TiN is even less defined. In both cases, the stoichiometry of the intermediate layer as well as the film changes after the thermal treatment. Electrical properties of these films will also be discussed.