In situ Observation of Initial Nucleation and Growth Processes in Supercritical Fluid Deposition of Copper

Abstract

The initial nucleation and coalescence of Cu by supercritical fluid deposition (SCFD) were monitored by measuring the surface reflectivity of visible white light. The reflectivity at 770 nm is sensitive to initial nucleation, thus, the nucleation and coalescence temperatures of Cu-SCFD can be easily monitored by this in situ technique. The nucleation temperature of Cu-SCFD was found to be independent of the precursor concentration, which suggests a strong adsorption and surface saturation of the source precursor at high concentration. A high H2 concentration up to 0.39 mol/L with Cu(tmhd)2 as a precursor can decrease the nucleation temperature from 215 to 180 °C. A high H2 concentration is also effective for realizing a smooth surface morphology of the deposited Cu film and for making the film thin at the coalescence stage probably because of the initial nucleation with a high number density. The fabrication of a 10-nm-thick continuous Cu film, which is required as a seed layer in ultralarge scale integration (ULSI), was successfully demonstrated with a high H2 concentration of 0.39 mol/L.