Fabrication of High-Quality α-Tantalum Films by Optimizing Working Pressure and Growth Temperature

Tantalum has attracted attention for its potential to enhance the performance of superconducting qubits. It exists with two distinct crystalline phases, α and β, with the α phase being particularly advantageous due to its larger superconducting gap, which attributes to longer qubit lifetimes. Thus, the fabrication of high-quality α-tantalum films is crucial for advancing tantalum-based superconducting qubits. While numerous studies have explored the applications of tantalum in superconducting qubits, the optimal conditions for depositing high-quality α-tantalum films are not fully understood. In this study, we focus on the role of residual film stress in influencing the quality of tantalum films. To optimize fabrication conditions, we investigated the effects of working pressure and substrate temperature on residual film stress. In addition, we characterized film quality by measuring the superconducting transition temperature (Tc) and residual resistivity ratio (RRR). Structural and surface properties of the films were further examined utilizing XRD and AFM, respectively.