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 film s having different microstructures rs ere investigated. Several etchin g solutions (HCl, HBr, and their mixtures with HNO3) were used in this study. We have found that ITO films containing a larger volume fracti on of the amorphous phase show higher etch rates than: those containin g a larger volume fraction of the crystal-line phase. Also, the crysta lline ITO films have shown a very good uniformity in patterning, and f allowing the etching no ITO residue (unetched ITO) formation has been observed. In contrast, ITO residues were found after the etching of th e films containing both amorphous and crystalline phases. We have also developed a process for the fabrication of the ITO with a tapered edg e profile. The taper angle can be controlled by varying the ratio of H NO3 to the HCl in the etching solutions. Finally, ITO films have been found to be chemically unstable in a hydrogen containing plasma enviro nment. 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 environm ent. 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 s uitable for a-Si:H TFT-LCD applications.