Fluorine-enhanced boron diffusion in germanium-preamorphized silicon

Abstract

Silicon wafers were preamorphized with 60 keV Ge+ or 70 keV Si+ at a dose of 1×1015 atoms∕cm2. F+ was then implanted into some samples at 6 keV at doses ranging from 1×1014 to 5×1015 atoms∕cm2, followed by B+11 implants at 500 eV, 1×1015atoms∕cm2. Secondary-ion-mass spectrometry confirmed that fluorine enhances boron motion in germanium-preamorphized materials in the absence of annealing. The magnitude of boron diffusion scales with increasing fluorine dose. Boron motion in as-implanted samples occurs when fluorine is concentrated above 1×1020atoms∕cm3. Boron atoms are mobile in as-implanted, amorphous material at concentrations up to 1×1019atoms∕cm3. Fluorine directly influences boron motion only prior to activation annealing. During the solid-phase epitaxial regrowth process, fluorine does not directly influence boron motion, it simply alters the recrystallization rate of the silicon substrate. Boron atoms can diffuse in germanium-amorphized silicon during recrystallization at elevated temperatures without the assistance of additional dopants. Mobile boron concentrations up to 1×1020atoms∕cm3 are observed during annealing of germanium-preamorphized wafers.