Article ID: 2012-0018
Highly reliable gate stack systems using a high-k dielectric thin film such as a hafnium dioxide film are indispensable for the development of ULSI (Ultra-Large-Scale Integration) devices. In this study, the degradation mechanisms of the electronic reliability of hafnium dioxide dielectric film caused by point defects such as oxygen vacancies and carbon interstitials was investigated by using quantum chemical molecular dynamics method. The magnitude of the band gap of the HfO2-x, which is hafnium dioxide with oxygen vacancies, decreased drastically from 5.7 eV to about 1.0 eV due to the generation of donor states within the band gap of hafnium dioxide. When a carbon atom as the impurity was introduced in HfO2 film, carbon impurity states (donor and acceptor) formed in the band gap of hafnium dioxide. The band gap calculated from the energy difference between the donor and acceptor decreases to 1.6 eV. The estimated changes of the magnitude of the band gap due to the point defects were validated by experiments using synchrotron radiation photoemission spectroscopy. We conclude therefore, it is very important to minimize point defects in the hafnium dioxide dielectric film in order to ensure the electronic performance and reliability of MOS transistors.
