Photoelectron spectroscopy studies of chemical vapor deposition of Ta from a TaF₅ precursor on Si and SiO₂ substrates

Abstract

The increasing need for metallization of microelectronic structures involving deep trenches and high aspect ratio features has sparked considerable interest in chemical vapor deposition metallization schemes. In this work the results of photoemission investigations of the substrate-driven reduction of TaF5 to Ta metal on Si(111) and SiO2 substrates are reported. At moderate temperatures the reaction showed no selectivity between these two substrates, in contrast to the process with the similar molecule WF6. At 400°C metallic Ta films could be grown on both Si and SiO2; however, x-ray photoelectron spectroscopy measurements show that the bonding of the film to Si(111) is dominated by fluorine atoms at the interface, whereas film growth on SiO2 tends to form an oxide interface with TaOF3 stoichiometry. Annealing of the deposited film to about 700°C leads to Si diffusion to the surface which is accompanied by the release of fluorine from the film. The deposition of TaF5 on Si(111) at 250°C results initially in a partly dissociative metallic deposition followed by a non-dissociative molecular chemisorption. Our experiments suggest the Si substrate to be reactive enough at the initial state of the deposition to break up theTaF5 molecule but that the process is quickly self-passivating.