Impact of Annealing on Contact Formation and Stability of IGZO TFTs

Thursday, May 15, 2014: 10:50
Manatee, Ground Level (Hilton Orlando Bonnet Creek)
T. Mudgal, N. Walsh (Rochester Institute of Technology), R. G. Manley (Corning Incorporated), and K. D. Hirschman (Rochester Institute of Technology)
Oxide semiconductors are candidate materials to replace amorphous silicon in thin-film transistors (TFTs) for LCD and OLED backplanes where the demand on performance is increasing. Indium-Gallium-Zinc-Oxide (IGZO) has shown promise because it exhibits high electron mobility and can utilize the existing fabrication infrastructure for flat-panel display manufacturing.  However the acceptance of IGZO requires exceptional uniformity and stability in device performance.  The necessity to anneal sputtered IGZO for improved device operation has been widely established; however the temperature, gas ambient, and process integration details vary. 

In this work, bottom-gate top-contact TFTs are fabricated using sputtered IGZO.  Molybdenum and aluminum were investigated as contact metals which defined the working source/drain electrodes.  Annealing processes applied either before or after metal deposition were investigated.  Annealing was done at 400 °C in various gas ambients including air, oxygen, nitrogen, forming gas (5% H2 in N2) and vacuum.  Channel passivation materials including SiO2 and Al2O3 were also investigated.  The annealing ambient and arrangement of process steps were found to have a significant influence on the contact behavior and the uniformity and stability of electrical characteristics.  These details have a significant impact on circuit operation, which will be discussed along with results of test circuits including inverters and ring oscillators.