P-61: A Study on the Galvanic Reaction between Cu and Mo as Well as MoW for TFT-LCDs by Using a Zero-Resistance Ammeter

Recently, copper metallization has been widely developed in TFT-LCD industry, because of its lowest electrical resistivity compared to aluminum and its alloys. In addition, the copper metallization becomes a more significant issue in a high frequency driving technology for large sized TFT-LCD panel. Since copper has a low adhesion force against the glass substrate, copper is inevitably used with an aid of an adhesive metal layer such as Ti, Ta and Mo. When dissimilar metals like copper and molybdenum are exposed together in a wet etchant, a typical galvanic reaction occurs and this results in an undercutting of copper line or partial stains on the metal surface after drying. The suitable taper angle of Cu line is difficult to obtain especially coupled with pure molybdenum. Such failures often lead to a bad performance of thin film transistor and the display quality. There are many literatures related to the copper metallization for TFT. However, a systematic approach on the galvanic reaction occurred in copper multilayered system has not been made. In this work, we investigated a feasibility of molybdenum alloy film (MoW) for copper metallization on the basis of the thin film analysis and the advanced electrochemical techniques such as Zero Resistance Ammeter (ZRA) method.