A barrierless Cu gate was proposed to fabricate the TFT-LCD. The wholly Cu-based gate is achieved by applying a Cu-alloy film to improve the poor adhesion of Cu to the glass substrate. The taper angle of Cu/Cu-alloy gate can be easily controlled by using the new Cu etchant. We have developed 1.8" panels with the barrierless Cu gate. Without capping any additional Cu barrier, the TFT characteristics and the reliability of the Cu gate TFT were the same as the one with the conventional metal gate such as Al and its alloys.

It was found that the extremely high contact resistance between Cu and ITO is caused by the damage of Cu during the via hole etching using SF 6 and O 2 plasma. TEM and XPS analysis indicate that an etching by-product composed principally Cu 2 O was formed on the Cu film after the via etching. The result of a 3-level 4-factor Taguchi design showed that SF 6 /O 2 ratio is the key parameter for the Cu dry etching. The Cu etching rate increases with decreasing the SF 6 /O 2 ratio. By a via etching with high SF 6 /O 2 , Cu 2 O formation could be suppressed. The via contact resistance between Cu and ITO could be improved as same as that in the conventional Al gate metal.