Raman scattering application was introduced to directly probe the depth profile of structural changes in a very thin surface layer of $F^+$-implanted Si by use of a single $Ar^+$ laser(488nm) excitation. The results of Raman scattering and sheet resistance measurement showed an unusual annealing behavior of the $F^+$-implanted Si:In the range of annealing temperature $T_a$ from 200℃ to 400℃, disordering was observed to increase with increasing $T_a$ but a stronger trend of ordering with $T_a$ increasing further above 400℃. This abnormal behavior could be explained as due to competition between the ordering effect of thermal annealing with increasing $T_a$ and the disordering effect of the implanted fluorine ions randomly breaking the Si-Si crystal bonds in the surface diffusion layer.
The annealing kinetics of $BF_2^+$ implanted Si was studied by Raman scattering. Heavily doped (above $5E15cm^{-2}$) Si needs higher rapid thermal annealing(10 sec) temperature than 900℃ in order to activate boron. Fully annealed Si showed red shift in a crystal Si Raman band and its FWHM value was increased. This means that activated boron gives tensile stress to the crystal lattice and induces shallow level defect states effecting FWHM value increasing. It was also known that sheet resistance measurement was not sensitive to the short range disorder. Raman intensity was decreased with increasing doping level due to the increased hole absorption of the incident light.
Boron diffusion was studied using the heavily $BF_2^+$ implanted Si by secondary ion mass spectroscopy. Boron enhanced diffusion occurred abnormally in the excess Si rich region below the amorphized layer at low temperature (300℃). This was explained by the diffusion model which says boron diffuse via an intermediate species: B+I → $B_i$. It is believed that fluorine do some role enhancing boron diffusion even at the low annealing temperature like 300℃ because it was known that boron enhanced diffusion occurred at annealing temperature above 700℃. It can be explained like that fluorine hinders interstitial Si growing into large size clusters which need high temperature annealing to dissociate into again freely migrating species. In fact, exponential-like diffusion profile of fluorine can be analyzed by a model diffusing via a F-I complex. This complex consumes the interstitial Si resulting in small Si clusters which could be dissociated at low annealing temperature. This result supports the fact that boron diffusion could be suppressed by co-implantation of halogen atoms.
