Deposition of Cu thin films from supercritical carbon dioxide using hexafluoroacetylacetnatecopper

Common deposition techniques for the metallization of ultra-large scale integrated circuits utilizes vapor (physical/chemical vapor deposition) or liquid (e.g. electro-chemical deposition). This paper reports the use of supercritical CO2 fluids as a new medium for depositing Cu thin films, where Cu is grown from a metalorganic precursor dissolved in the fluid. Hexafluoroacetylacetnatecopper (CuII (hfac)2) was used as the precursor, and depositions were carried out at pressures of 10-15 MPa and temperatures of 180-400 °C. We observed preferential growth of Cu on conductive substrates, a lower deposition temperature of 180 °C by about 100 °C than typical values reported for Cu chemical vapor deposition from CuII (hfac)2. The temperature dependence of the deposition rate was further studied and the activation energy for the growth was determined at 0.42 ± 0.12 eV. Basic film characterization was also performed; X-ray photoelectron spectra of the films showed pronounced metallic Cu peaks and trace level of impurity elements, and X-ray diffractometry showed (111) film texturing. Copper filling into nano high-aspect-ratio features was also demonstrated. Finally, a critical role of the solvent capability of supercritical CO2 on the film quality was discussed with comparative depositions using supercritical Ar.