P-56: Eco-Friendly Copper Metallization for IGZO and LTPS with New Molybdenum Barrier Layer

Abstract

As copper metallization processes have been widely adopted in the panel display industry, waste treatment costs including those for fluorine ions in copper wet etchant have also dramatically increased. The reduction of fluorine ions in copper metallization processes will be a key eco-friendly business issue in the near future. For this paper, new molybdenum alloy as a copper barrrier layer for IGZO and LTPS applications was developed that can be easily wet-patterned in copper wet etchant without etch residue. First, the effects of metal electrodes on the electrical performance of back channel etching type amorphous In-Ga-Zn-O thin film transistors were studied. Then, a secondary ion mass spectroscopy depth analysis revealed that the detected molybdenum content on the IGZO surface after wet patterning experienced a ten-fold reduction compared to pure molybdenum. In addition, new molybdenum alloy showed better thermal resistance properties compared to pure molybdenum. After the Mo alloy/copper/Mo alloy tri-layers were annealed at 400 °C for 1 hour, the electrical resistance decreased from 5.7 µohm-cm to 3.2 µohm-cm, while the pure molybdenum tri-layer showed a dramatic increase after thermal annealing. The reduced molybdenum residue after wet patterning also influenced the electrical properties of the back channel etching type IGZO TFTs. The mobility measured between 10~14 cm2/V.sec and the contact resistance was about 0.5 Mohm. Both value were comparable to reported value.