Investigation of tantalum films growth for coplanar resonators with internal quality factors above ten million

Alpha-tantalum on silicon is a promising platform for high-coherence superconducting quantum circuits. However, the growth mechanism of alpha-tantalum on silicon remains poorly understood. We present a comprehensive study on alpha-tantalum film growth on various substrates. The decisive role of a substrate material Debye temperature on the phase selection mechanism in tantalum film growth is experimentally confirmed, contradicting the prior assumptions on substrate temperature influence. Crucially, we confirm that alpha-tantalum starts growing only after a 7–10- nm-thick beta-tantalum sublayer. It results in ranging the critical temperature of α-Ta films from 3.77 to 4.39 K for the total thickness from 20 to 150 nm, respectively. Finally, we compared high-quality Al and Ta coplanar resonators on silicon, demonstrating compact tantalum resonators (4/10.5/4 μm) with an internal quality factor exceeding 10 × 106 at single-photon excitation powers.