Development of an All-Wet-Etch Process Chemistry for the Patterning of Metal Conductors in Igzo Thin-Film-Transistors

Abstract

Here, we discuss the development of an all-wet back-channel etch process chemistry with high metal selectivity that is capable of shaping the structures of an IGZO TFT to customer specifications. Our approach involves a two-step etching process that first selectively removes only the metal conductor (Cu) while temporarily stopping at the underlying metal adhesion layer (Mo or Ti). The chemistry then selectively removes the metal adhesion layer with minimal impact to the IGZO semiconductor. By pursuing a two-step approach, where each chemistry is designed to target a specific metal with high selectivity, the risk of excessive metal undercutting generally associated with wet-etch techniques can be mitigated. Furthermore, those issues associated with a dry-etch (i.e., degraded electron mobility and high threshold voltages due to structural damage to the semiconductor active layer) can be avoided.