Ge-friendly gate stacks: Initial property and long-term reliability

Abstract

This work presents specific exploration on the novel gate stack strategies for the intriguing Ge p-MOSFET, where high pressure oxidation (HPO) process is utilized for sufficient oxidation and thus fewer oxygen vacancies, while yttrium doping is developed to strengthen the dielectric bonding for higher ruggedness. Superior gate controllability and stability have been achieved correspondingly, where then detailed comparison on the gate dielectric reliability is conducted. The HPO based GeO₂ gate stack exhibits larger susceptibility to the gate bias stress, and could even breakdown under negative bias, which has been attributed to the local bond breakage that facilitates the irreversible network change. The yttrium-doped GeO₂, on the other hand, presents impressive ruggedness against gate bias stress. Based on detailed bond breakage analysis, cation-doping in GeO₂ is suggested to be effective in enhancing the bond rigidness, promising for a wider safe operation range for the gate bias in Ge MOSFET.