Influence of Extension Formation Process on Indium Halo Profile

Abstract

Halo doping is one of the key technologies for MOSFET doping design. However, Halo profile is strongly affected by the S/D (Source and Drain) formation process. We have investigated variations in Indium (In) Halo depth profiles due to differences in the S/D formation process. In order to minimize TED (Transient Enhanced Diffusion) of In, In must be implanted after S/D implantation that accompanies the formation of the amorphous layer. The mechanism of redistribution of In atoms is discussed based on SIMS (Secondary Ion Mass Spectroscopy) and TEM (Transmission Electron Microscopy) evaluations. is very slight even after 60 s RTA. This result shows that In TED (Transient Enhanced Diffusion) has a sub-second duration, and further diffusion is quite slower than this TED. Figure 4 shows the comparison between the In-1st and Sb-1st cases. The In tail profile for the Sb-1st is slightly steeper than that for the In-1st. Figure 5 shows the comparison between the 1-step RTA and 2-steps RTA for the Sb-1st condition. The In pileup peak found at the extension tail for the 1-step RTA is higher than that for the 2-steps RTA, and the In tail profile for the 1-step RTA is steeper than that for the 2-steps. From the point of view of the device fabrication, the Sb-1st-1-step was the best because it had the steepest In profile. These In behaviors are also observed for the As extension case as shown in Fig. 6, which implies that obtained results are not due to specific features of Sb. 4. Discussion Cross-sectional TEM micrographs for the Sb-1st-1-step and Sb-1st-2-steps are shown in Figs. 7 and 8, respectively. Many EOR (End of Range) defects were observed in the specimen for the 1-step, as shown in Fig. 7. However, the EOR defects were not found in the cross-sectional observation for the 2- steps. In these specimens, (311) defects were not observed. This supports the sub-second TED shown in Fig. 3, because (311) defects that consist of interstitial Si gradually decompose and arise in TED. The depth of the In pileup observed in the SIMS profile is almost the same as that of the EOR defects. In seems to aid in the formation of, and be trapped by, the EOR defects. This trapping means a decrease in mobile In atoms that is one of the considerable causes of a steeper In profile for the 1-step annealing. In addition, if the interstitial Si atoms are also trapped by the EOR defects, TED is weakened. In the case of the 2-steps annealing, EOR defect density is so small, and the loss of mobile In and interstitial Si atoms is so limited, that profile broadening in the tail region is apparent. The In diffusion model described here is summarized in Fig. 9. 5. Conclusion The In Halo profile was evaluated in relation to the extension formation process. The In displayed very fast TED at the early stage of RTA, and the consequent diffusion was much slower. Sb implantation before In implantation effectively reduced In diffusion. The 2-steps annealing reduced the EOR defects; however, In diffusion was apparent. Consequently, the best process order for obtaining a steep In profile was extension implantation, Halo implantation and RTA.