Redistribution of Fluorine from BF2+ Implants in MOS Structures

The thermal redistribution of fluorine from 111 keV BF2⁺ molecular ion implants in (100) Si and 56 nm thick thermally grown SiO2 films on Si substrates has been studied using the Nuclear Resonance Broadening (NRB) technique. Vacuum annealing at temperatures up to at least 700°C lead to no loss or redistribution of fluorine from either the pure Si or oxidised Si samples. Fluorine diffusion took place for temperatures of 900°C and above. At these temperatures fluorine was lost from the Si samples but agglomerated, most probably at the SiO2/Si interface in the oxidised samples.