Thermal stability comparison of TaN on HfO2 and Al2O3

Changes in gate stacks (TaN/high-kappa/SiO2/Si) are investigated during thermal processing using in situ Fourier transform infrared spectroscopy. Ta-O bonds, present in the initial tantalum nitride films, are crystallized in contact with HfO2 at 700-800 degrees C and completely dissociate at 900 degrees C, resulting in a microcrystalline TaNx phase. The TaN remains amorphous, however, with Al2O3 as the underlying dielectric layer. A partial reduction into a metallic Ta occurs after dissociation of Ta-N and Ta-O bonds, and Al2O3 decomposes at 700 degrees C. Dissociated Al atoms diffuse into all the neighboring layers to form silicate and Ta- and N-bound Al.