INVESTIGATION ON THE DISTRIBUTION OF FLUORINE AND BORON IN POLYCRYSTALLINE SILICON SILICON SYSTEMS

The behaviors of fluorine in BF2+ implanted polycrystalline silicon (poly-Si) on silicon have been investigated in the annealing temperature range of 850 to 1100 degrees C. The distribution of fluorine atoms as functions of temperature and time have been monitored by the secondary ion mass spectroscopy (SIMS) and cross-sectional transmission electron microscopy (XTEM). The XTEM micrographs revealed that fluorine bubbles are distributed in the poly-Si and at the original poly-Si/Si interface after annealing. The locations of bubbles were found to correspond to the fluorine peaks in the SIMS depth-concentration profiles. The presence of the boron peak at the original poly-Si/Si interface is attributed to the gettering of boron atoms by the fluorine bubbles. Moreover, the boron profiles in the silicon substrates are sensitive to thermal budget due to the pileup of fluorine atoms at the poly-Si/Si interface. The pileup of fluorine at the poly-Si/Si interface leads to an enhancement of epitaxial regrowth of poly-Si films and. the formation of fluorine bubbles. Consequently higher surface dopant concentration and deeper junction depth were obtained.