Improvement of IGZO BTI for DRAM Cell application by heat treatment and recovery effect

Toward vertical channel transistor (VCT) DRAM, Indium-Gallium-Zinc Oxide (IGZO) is the one of the best candidates with stackable and ultra-low off current against Si buried cell array transistors (Si BCAT). However, the IGZO has a huge obstacle of trade-off between on-current performance and bias temperature instability (BTI) of IGZO due to oxygen vacancy (Vox) and hydrogen in IGZO. In this study, we improved the BTI of IGZO without on-current trade-off, and further ensured the reliability margin through a recovery model with DRAM Cell refresh. The Negative Bias Temperature Instability (NBTI) and Positive Bias Temperature Instability (PBTI) of IGZO were degraded by Vox and hydrogen. High temperature IGZO deposition reduced Vox, and the NBTI dVth of IGZO were improved by ×1 0 times. PBTI dVth reduced by ×3 times through hydrogen outgassing by degas in vacuum. Furthermore, AC BTI of IGZO was investigated to pre-validate actual DRAM Cell operation mode. In actual DRAM refresh, the NBTI dVth reduced by 38% with multiplying ×5 lifetime. PBTI dVth decreased by 43% with decreasing PBTI duty. Especially, we found that the recovery effect of 80% of IGZO was much larger than 25% of Si because its shallow trap and acceleration effect of Vpp.