Wet Etching of TiO2-Based Precursor Amorphous Films for Transparent Electrodes

We investigated wet etching of Nb-doped anatase TiO 2 (TNO) transparent conducting thin films and their precursors in an amorphous phase deposited by rf sputtering on glass substrates. The polycrystalline TNO films showed a very low etching rate of less than 0.06 nm/min in concentrated sulfuric acid (H 2 SO 4 ) even at elevated temperatures up to 95 °C. In contrast, H 2 SO 4 etched the precursor films at a rate of 1.4 nm/min at 95 °C. The etching rate of the amorphous films followed the Arrhenius equation, leading us to conjecture that a much higher etching rate of ${\sim}230$ nm/min can be achieved at 170 °C. These results indicate that wet-etching of precursor amorphous films prior to crystallization represents a practical and low-cost lithographic technique for patterning TiO 2 -based transparent electrodes.