Formation of voids in Ti-salicided BF2+-doped submicron polysilicon lines

The physical characteristics and distribution of voids in TiSi2/p(+)-Si sys tem as a function of polycrystalline silicon (polySi) linewidths were inves tigated in detail using scanning electron microscopy, cross-sectional trans mission electron microscopy, and the focused ion beam technique. Surface an d subsurface voids were found in Ti-salicided BF2+-implanted polycrystallin e silicon (polySi) lines that were annealed at temperatures ranging from 65 0 to 850 degrees C. Most of the subsurface voids were found in the TiSi2 fi lm as well as at the TiSi2/polySi interface. The void density, shape irregu larity, and void size increase with decreasing polySi linewidth, especially when it is smaller than 0.24 mu m, indicating that stress associated with narrow polySi lines may play an important role in the voiding phenomenon. I t was also shown that the TiN film overlying the TiSi2 film and the etch-ba ck process could not be responsible for the void formation process. Instead the absence of voids in B+-implanted polySi and the segregation of fluorin e into the TiSi2/polySi and TiN/TiSi2 interfaces from BF2+-implanted polySi after the first salicidation rapid thermal annealing suggest a fluorine-as sisted voiding mechanism. (C) 2000 American Institute of Physics. [S0021-89 79(00)06912-7].