The selectivity of Cu deposition from bis(hexafluoroacetylacetonato)Cu(II) on SiO2 patterned with a Pt seeding layer was studied as a function of the reagent gas mixt. On Pt, the Cu film growth rate increases with the amt. of H2O vapor in the gas flow, and is independent of the chem. nature of the carrier gas used (H2 or He). The selectivity of the Cu deposition is significantly improved when using He rather than H2 as carrier gas, esp. at high H2O vapor concns. where rapid film growth can be obtained.