Ion behavior impact on ITO thin film fabrication via DC magnetron sputtering with external anode

Abstract

“Sputtering damage” arising from high-energy negative ions plays a pivotal role in shaping the characteristics of indium tin oxide (ITO) thin films deposited through direct-current magnetron sputtering (DCMS). To mitigate this issue, we employ DCMS with an external anode. The increment in anode bias VA from 0 to +60V effectively diminishes the average kinetic energy of negative ions such as O−, O2− and InO− by reducing the cathode voltage. Additionally, the flux of positive ions (e.g., Ar+, In+, Sn+, O+) increases and their ion energy distribution functions (IEDFs) exhibit supplementary peaks at plasma potentials. Both facilitate film crystallization, as evidenced by the structural transition from subgrain to grain formations. Heightened surface roughness markedly enhances optical transmittance. Due to a reduced oxygen sticking coefficient, films grown with higher VA values exhibit increased oxygen vacancies, which serve as the primary charge carriers for ITO films. Consequently, ITO films attain their lowest resistivity (7.81×10−4Ωcm) and highest optical transmittance (78.71 %) at VA = +60V. This investigation underscores the significant influence of the external anode bias on both ion behavior and film growth, providing a viable approach to enhance the electrical and optical properties of ITO films.