Sputtered Ta films (60 nm) were deposited at room temperature onto selected substrates, including silicon, SiO2, porous methyl silsesquioxane (porous MSQ), parylene-N (Pa-N) caulked porous MSQ, benzocyclobutene (BCB), and SiLK layers. It was observed that the Ta structure after deposition mainly depends on the underlayer surface chemistry. beta-Ta with a resistivity of similar to 130-160 mu Omega cm and an average grain size of similar to 20 nm was observed after sputter depositing 60-nm-thick Ta films onto the oxygen-rich materials of native oxide of Si, SiO2, and porous MSQ. alpha-Ta with a much lower resistivity (similar to 35 mu Omega cm) and an average grain size of similar to 16 nm was observed after sputter deposition of Ta onto a substrate with a 4-nm-thick hydrocarbon Pa-N film on porous MSQ. a-Ta was also formed when sputter depositing on the hydrocarbon BCB and SiLK lokw-K dielectrics. The lattice constants of the alpha-Ta films were slightly larger (3.310-3.351 angstrom) than those of the bulk Ta (3.305 angstrom). (c) 2006 American Vacuum Society.