Vacancy-fluorine complexes and their impact on the properties of metal-oxide transistors with high-k gate dielectrics studied using monoenergetic positron beams

摘要

Vacancy-fluorine complexes in metal-oxide semiconductors (MOS) with high-k gate dielectrics were studied using a positron annihilation technique. F~+ ions were implanted into Si substrates before the deposition of gate dielectrics (HfSiON). The shift of threshold voltage (V_(th)) in MOS capacitors and an increase in Fermi level position below the HfSiON/Si interface were observed after F~+ implantation. Doppler broadening spectra of the annihilation radiation and positron lifetimes were measured before and after HfSiON fabrication processes. From a comparison between Doppler broadening spectra and those obtained by first-principles calculation, the major defect species in Si substrates after annealing treatment (1050℃, 5 s) was identified as vacancy-fluorine complexes (V_3F_2). The origin of the Vth shift in the MOS capacitors was attributed to V_3F_2 located in channel regions.