Improving IGZO transistor PBTI reliability with hydrogen anneal achieving overdrive voltage of 1.2V for a lifetime of 5 years at 95°C

Abstract

We propose a novel annealing scheme for IGZO-based transistors, which enables the hydrogen resilience needed to meet the reliability specs for embedded DRAM applications: an overdrive voltage of 1.2V for a lifetime of 5 years at 95°C. First, we show that standard IGZO compositions (~1:1:1 at%) and In-Poor (In~10%) suffer from opposite reliability limitations. Standard IGZO only meets the reliability target for the +ΔVth component caused by electron trapping, In-Poor only meets the reliability target for the -ΔVth component caused by H-doping. We ascribe the observed ~10x larger +ΔVth in In-Poor films to a closer energetic alignment between IGZO Ec and Al2O3 trap bands. Second, we describe how a combination of hydrogen (FGA) and oxygen anneals reduces the H-doping process during PBTI stress by ~30x, without a performance penalty. This reliability improvement is reasoned to be due to excess oxygen scavenging during FGA, minimizing the preferential bonding sites of hydrogen released by the gate-dielectric during PBTI at high temperatures.