Patterning of transparent conducting oxide thin films by wet etching for a-Si:H TFT-LCDs

The patterning characteristics of the indium tin oxide (ITO) thin films having different microstructures rs ere investigated. Several etching solutions (HCl, HBr, and their mixtures with HNO3) were used in this study. We have found that ITO films containing a larger volume fraction of the amorphous phase show higher etch rates than: those containing a larger volume fraction of the crystal-line phase. Also, the crystalline ITO films have shown a very good uniformity in patterning, and fallowing the etching no ITO residue (unetched ITO) formation has been observed. In contrast, ITO residues were found after the etching of the films containing both amorphous and crystalline phases. We have also developed a process for the fabrication of the ITO with a tapered edge profile. The taper angle can be controlled by varying the ratio of HNO3 to the HCl in the etching solutions. Finally, ITO films have been found to be chemically unstable in a hydrogen containing plasma environment. On the contrary, aluminum doped zinc oxide (AZO) films, having an optical transmittance and electrical resistivity comparable to ITO films, are very stable in the same hydrogen containing plasma environment. In addition, a high etch 1 ate, no etching residue formation,and a uniform etching have been found for the AZO films, which make them suitable for a-Si:H TFT-LCD applications.