Interface formation and reactions at Ta-Si and Ta-SiO2 interfaces studied by XPS and ARXPS

Tantalum-based materials are of great interest as barriers against copper diffusion. For future microelectronic devices these barriers must shrink in thickness. Therefore, a substantial influence of the barrier's interfaces on its properties can be expected. We have deposited tantalum from sub-monolayer coverage up to about 10 nm thick films by DC magnetron sputtering onto silicon and silicon dioxide substrates in a UHV preparation chamber attached to the XPS chamber since Ta oxidizes even at low oxygen partial pressure. XPS measurements revealed interfacial reactions in both systems. In the system Ta on Si TaSi2 formation and in the system Ta on SiO2 Ta suboxide due to SiO2 reduction and eventually Ta5Si3 formation were found to take place. Based on these observations film growth models were developed. Using these models ARXPS measurements of selected samples were quantified to yield their structures (layer thicknesses and stoichometries)