Summary

This chapter reports on the reliability assessment of Ge gate stacks with promising initial electrical properties, focusing on the pre-existing trap and trap generation under a constant E_stress. Initial Ge gate stack properties do not necessarily secure the high reliability robustness. It is found that the pre-existing hole traps are one of the most critical concerns in GeO₂/Ge gate stack, which might be attributed to the V_O formed during the gate stack process. The HPO-GeO2 and M-GeO2 can effectively reduce the VO formation during the gate stack process, thereby reduce pre-existing hole trap density.

However, under an elevated stress field, the trap generation becomes a major concern regardless of the initial properties because Ge-O bond are highly susceptible to bond breaking and ion displacement by electric field. Small amount Y-GeO2 or Sc-GeO2

significantly reduces the trap generation in Ge gate stacks without the interface deterioration. This result is understandable from the increase of average coordination number (N_av) in the modified GeO₂ network by doping.

The reliability of sub-nm EOT YScO3/Y-GeO2/Ge and HfO2/Y-GeO2/Ge gate stacks are also examined. The selection of top high-k dielectric also has a significant impact on the reliability degradation. YScO3/Y-GeO2/Ge shows better long term reliability thanks to its defect free characteristics.

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