Reactive Deposition of Conformal Palladium Films from Supercritical Carbon Dioxide Solution

High-purity palladium films were deposited onto Si wafers and polyimide by the reduction of organopalladium compounds in supercritical CO2 solution using a batch process at temperatures between 40 and 80 °C and pressures between 100 and 140 bar. Hydrogenolysis of π-2-methylallyl(cyclopentadienyl)palladium(II) in CO2 at 60 °C is complete in less than 2 min, yielding continuous, 100−200 nm thick, reflective films and the benign, fully hydrogenated ligand decomposition products, cyclopentane and isobutane. Analysis of the deposited films by X-ray photoelectron spectroscopy indicates that they are free of ligand-derived contamination. Deposition of thin films on patterned silicon wafers having feature sizes as small as 0.1 μm wide by 1.0 μm deep is strictly conformal, including uniform coverage of the lower corners and bottoms of the trenches. Deposition by hydrogenolysis of palladium(II) hexafluoroacetylacetonate also yields high-quality films while deposition using π-allyl(2,4-pentanedionato)palladium(II) is sensitive to fluid-phase decomposition of the precursor and yields nonuniform deposits.