27.3: Invited Paper: Electrochemical study on wet etching of copper/molybdenum alloys in thin film transistors

As copper metallization process is widely adopted by Flat panel display industry, cost for waste treatment such as fluorine ions in copper wet etchant also dramatically increased. Reduction of fluorine ion in copper metallization process, will be a key environment friendly business issue in near future. In this paper, we developed new MoK copper barrrier layer for IGZO and LTPS application which can be easily wet‐patterned in copper wet etchant without etch residue. The effects of metal electrode on the electrical performance of back channel etching type amorphous In‒Ga‒Zn‒O thin film transistor have been studied. From secondary ion mass spectroscopy depth analysis, the detected molybdenum content on IGZO surface after wet patterning was greatly reduced by 10 times compared with pure molybdenum. In addition, MoK showed a better thermal resistance properties compared with pure molybdenum. After the MoK/copper/MoK tri‐layers were annealed at 400°C for 1 hour, the electrical resistance was decreased from 5.7 uohm‐cm to 3.2 uohm‐cm while pure molybdenum tri‐layer showed dramatic increase after thermal annealing. The reduced molybdenum residue after wet patterning also influenced the electrical properties of back channel etching type IGZO TFTs. The measured mobility lied between 10∼14 cm2/V.sec and contact resistance was about 0.5 Mohm which is comparable with reported values. The enhanced device performance and thermal stability were interpreted in terms of electron density change and intermetallic compound formation at Cu/MoK interface.