Chemistry of diffusion barrier film formation:: Adsorption and dissociation of tetrakis(dimethylamino)titanium on Si(100)-2 x 1

Tetrakis(dimethylamino)titanium (TDMAT) is one of the most prominent precursors for deposition of thin diffusion barrier films onto semiconductor substrates for microelectronic applications. Adsorption and dissociation of this compound on a Si(100)-2 x 1 surface is studied by a combination of density functional calculations and infrared spectroscopy. Our computational investigation suggests that initial interaction occurs through the nucleophilic attack of a surface silicon atom by the lone pair of nitrogen. This molecularly adsorbed state (where the N atom attached to the surface is tetra-coordinated) is found to be a local minimum, and further transformation leads to the dissociation through scission of either the N-Ti or the N-C bond. Dissociation of TDMAT is permitted kinetically if it occurs through the scission of the N-Ti bond, while scission of an N-C bond is kinetically hindered despite the thermodynamic stability of the structure produced. In view of its amine-like behavior upon adsorption, TDMAT was expected to be molecularly adsorbed at cryogenic temperatures but dissociated at room temperature. These two facts are confirmed by infrared spectroscopy. Dissociation pathways involving two neighboring Si-Si dimers of the Si(100)-2 x 1 surface were considered as well, and the formation of an interdimer N-Ti bridge is found to be energetically possible. The elucidation of the mechanism of TDMAT adsorption holds the promise of a better understanding of the initial steps of thin film growth.