Etching characteristics and surface properties of fluorine-doped tin oxide thin films under CF4-based plasma treatment

Abstract

Owing to their low-cost, high-temperature processability, and excellent optoelectronic properties, fluorine-doped tin oxide (FTO) films are widely used as transparent conductive materials to replace indium-tin-oxide films. Dry etching is increasingly preferred for the patterning of FTO films considering the high-resolution patterning process required for microdevice applications. This study investigates the dry etching of FTO thin films using CF4-based plasma treatment and analyzes the changes in the etching characteristics and surface properties based on various conditions. The highest etching rate was observed under pure CF4 conditions, indicating that the chemical etching effect is the primary mechanism during the etching process. Based on the X-ray photoelectron spectroscopy and optical emission spectroscopy results, we determined that the etching of the FTO thin film was caused by the CFX radical in the CF4-based plasma. Additionally, the X-ray diffraction results indicate that the plasma etching increased the crystal defects in the FTO film. The etching process smoothened the surface morphology of the FTO film, and the transmittance and bandgap energy were slightly changed as a function of the etching conditions. Additionally, the resistivity of the FTO film improved slightly. The obtained results can benefit the development of high-performance optical devices that use FTO as transparent electrodes.