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Sequential 3-D stacking of multiple CMOS device tiers in a single fabrication flow requires the development of reliable high- ${k}$ /metal gate (HKMG) stacks at a reduced thermal budget (<525 °C). The omission of the customary high-temperature gate-stack annealing results in excessive dielectric defect densities. We have recently demonstrated on MOS capacitors the insertion of “defect decoupling” layers–LaSiOx for nMOS and Al2O3 for pMOS–at the interface between SiO2 and HfO2 as a promising approach to engineer the high- ${k}$ band lineup and minimize charge trapping for improved bias-temperature-instability (BTI) reliability. In this article, we demonstrate this approach in planar transistors, which allows assessing the impact of defect decoupling on carrier mobility. First, a comparative study on the impact of LaSiOx and Al2O3 insertion is performed, highlighting the different strategies for improving positive BTI (PBTI) and negative BTI (NBTI) reliability. Second, a comprehensive investigation on the effects of LaSiOx and Al2O3 insertion is conducted with a focus on BTI reliability and channel carrier mobility: a lack of penalty (Al2O3) or even improved carrier mobility (LaSiOx) is reported for the dipole-inserted gate stacks. Furthermore, we explore the simplified dual gate-stack integration for CMOS flow. A severe PBTI reliability penalty is observed if an Al2O3 layer (for hole trap decoupling) is deposited in the nMOS gate-stack, even if on top of the beneficial LaSiOx (for electron trap decoupling). In contrast, the pMOS gate-stack is found to be more tolerant to the presence of a residual LaSiOx layer on top of the beneficial Al2O3 layer, suggesting a viable strategy for the simplified dual gate-stack integration. Finally, the reliability improvement is validated also on a FinFET test vehicle. [ABSTRACT FROM AUTHOR]

In this work, we study oxide defects in various III-V/high-k metal-oxide-semiconductor (MOS) stacks. We show that the choice of a given starting measurement voltage with respect to the MOS flat-band voltage affects the observed capacitance-voltage hysteresis. We discuss how this behavior can be used to study the distribution of oxide defect levels. With the help of comprehensive experimental data, we show that Al2O3 and HfO2 have different hysteresis characteristics related to different oxide defect distributions. In case of an Al2O3/HfO2 bilayer stack with Al2O3 on the channel side (interfacial layer, IL), as the IL thickness reduces from 3 nm to 0 nm, the hysteresis behavior switches from the typical Al2O3 behavior to the one corresponding to HfO2. We link the characteristic behavior of two dielectrics to the defect level distributions inside their respective band-gaps through a simple energy-driven charging model. Based on the experimental data and simulation results, we show that Al2O3, despite having a lower peak defect density as compared to HfO2, shows a very wide, almost continuous distribution of defect levels across and around the InGaAs channel energy band gap. These results explain the often reported poor reliability of III-V devices with Al2O3-based gate stacks. [ABSTRACT FROM AUTHOR]