  Tantalum films incorporated into superconducting circuits have exhibited low
surface losses, resulting in long-lived qubit states. Remaining loss pathways
originate in microscopic defects which manifest as two level systems (TLS) at
low temperature. These defects limit performance, so careful attention to
tantalum film structures is critical for optimal use in quantum devices. In
this work, we investigate the growth of tantalum using magnetron sputtering on
sapphire, Si, and photoresist substrates. In the case of sapphire, we present
procedures for growth of fully-oriented films with alpha-Ta [1 1 1] // Al2O3 [0
0 1] and alpha-Ta [1 -1 0] // Al2O3 [1 0 0] orientational relationships, and
having residual resistivity ratios (RRR) ~ 60 for 220 nm thick films. On Si, we
find a complex grain texturing with Ta [1 1 0] normal to the substrate and RRR
~ 30. We further demonstrate airbridge fabrication using Nb to nucleate
alpha-Ta on photoresist surfaces. Superconducting resonators patterned from
films on sapphire show TLS-limited quality factors of 1.4 +/- 0.3 x 10^6 at 10
mK. Structural characterization using scanning electron microscopy, X-ray
diffraction, low temperature transport, secondary ion mass spectrometry, and
transmission electron microscopy reveal the dependence of residual impurities
and screw dislocation density on processing conditions. The results provide
practical insights for fabrication of high-performing technological devices
including qubit arrays, and guide future work on crystallographically
deterministic qubit fabrication.
