The columnar defect of hole etching in oxide process was investigated in this study. The reason or sources which is responsible for the columnar defect was revealed and corresponding measures for avoiding columnar defect were effectively established．The primary reason for producing columnar defect might be related to film structure, which can be deduced from the differences between two kinds of hole. After uncovering each layer of the film, columnar defect was detected in ITO layer. The result of scanning electron microscopy (SEM) showed that small particles appeared on the ITO layer after hole etching. Based on the above-mentioned mechanism of columnar defect formation, three solutions were attempted to solve the issue. ITO crystal cannot be etched by etching solution and residual ITO crystals will impede SiO2 etching, which will produce columnar defect. Once ITO crystal was formed, extending the etching time will not remove the columnar defect. Decreasing the thickness of ITO can partially eliminate the columnar defect while completely erasing the columnar defect and etching the ITO crystal can be achieved by increasing the etching gases in passivation layer etching process