Stable and high-quality Al-doped ZnO films with ICP-assisted facing targets sputtering at low temperature

FTS (facing targets sputtering) has been studied intensively for high-quality TCO films in low-temperature processes. In this study, we designed ICP-assisted FTS process for high-quality Al-doped ZnO film synthesis in a low temperature process. A one-turn ICP coil was installed a few cm above the upper target edge through which hydrogen was introduced and fully dissociated to the atomic radicals. The increase of ICP power caused heating and rarefaction of Ar gas and generated abundant hydrogen atoms and hydrogenated molecules. In FESEM analysis, the films synthesized with high ICP power showed high crystallinity. XPS was used to analyze the film structure. In O1s spectra, the low binding energy component located at ∼530.3 ± 0.4 eV corresponding to O²⁻ ions on the wurtzite structure of the hexagonal Zn²⁺ ion array increased with the ICP power, indicating good crystal quality. With increasing ICP power fixing while fixing the RF power at the cathode, the resistivity was observed to decrease to 5 × 10⁻⁴ Ω-cm. For thermal reliability tests, films were stored in an air-based chamber at 200 °C. The films synthesized without ICP showed rapid degradation in the electrical properties, while the films synthesized with high ICP power showed good stabilities with little change in the electrical properties after 30 h of storage in an oven. By adding hydrogen, the carrier concentration of the films increased, while the mobility did not change much. From these results, it is expected that hydrogen was incorporated into the film as a stable n-dopant by using an auxiliary ICP plasma source. (papers)