Formation of body-centered-cubic tantalum via sputtering on low-κ dielectrics at low temperatures

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. β-Ta with a resistivity of ∼130–160 μΩ cm and an average grain size of ∼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. α-Ta with a much lower resistivity (∼35 μΩ cm) and an average grain size of ∼16 nm was observed after sputter deposition of Ta onto a substrate with a 4-nm-thick hydrocarbon Pa-N film on porous MSQ. α-Ta was also formed when sputter depositing on the hydrocarbon BCB and SiLK low-κ dielectrics. The lattice constants of the α-Ta films were slightly larger (3.310–3.351 Å) than those of the bulk Ta (3.305 Å).