Formation of voids in Ti-salicided BF+ 2-doped submicron polysilicon lines

Abstract

The physical characteristics and distribution of voids in TiSi2/p +-Si system as a function of polycrystalline silicon (polySi) linewidths were investigated in detail using scanning electron microscopy, cross-sectional transmission electron microscopy, and the focused ion beam technique. Surface and subsurface voids were found in Ti-salicided BF+ 2-implanted polycrystalline silicon (polySi) lines that were annealed at temperatures ranging from 650 to 850 °C. Most of the subsurface voids were found in the TiSi2 film as well as at the TiSi2/polySi interface. The void density, shape irregularity, and void size increase with decreasing polySi linewidth, especially when it is smaller than 0.24 μm, indicating that stress associated with narrow polySi lines may play an important role in the voiding phenomenon. It was also shown that the TiN film overlying the TiSi2 film and the etch-back process could not be responsible for the void formation process. Instead the absence of voids in B+-implanted polySi and the segregation of fluorine into the TiSi2/polySi and TiN/TiSi2 interfaces from BF+ 2-implanted polySi after the first salicidation rapid thermal annealing suggest a fluorine-assisted voiding mechanism. © 2000 American Institute of Physics.