Low-Temperature Deuterium Annealing for High-Performance and Reliable Poly-Si Channel Thin-Film Transistors

Post-metallization annealing (PMA) is used in device fabrication to improve MOSFET performance and reliability and is typically carried out at 400 °C or higher. However, high-temperature PMA can result in unexpected junction modifications and dopant deactivation. As an alternative, low-temperature deuterium annealing (LTDA), which is performed at an annealing temperature 100 °C lower than the conventional PMA, is introduced. The LTDA effectively reduces the traps in the silicon channel and SiO2 dielectric [e.g., gate dielectric and buried oxide (BOX)] with a low-thermal budget. Poly-Si channel thin-film transistors (TFTs) are fabricated as test vehicles (TVs) to verify the impact of LTDA. The electrical characterization of subthreshold swing (SS), threshold voltage ( ${V}_{\text {TH}}$ ), ON-state current ( ${I}_{ \mathrm{\scriptscriptstyle ON}}$ ), OFF-state current ( ${I}_{ \mathrm{\scriptscriptstyle OFF}}$ ), and gate leakage ( ${I}_{\text {G}}$ ) is comparatively studied with and without LTDA. The long-term reliability of the device following LTDA under hot-carrier injection (HCI) stress condition is confirmed. Finally, further investigation was carried out on the reduced sheet resistance ( $R_{\text {sheet}}$ ) and surface roughness of the poly-Si gate. The improvement of poly-Si roughness under diluted deuterium ambient is investigated for the first time.