Cavities and dislocations induced in silicon by MeV He implantation

We implanted n-type silicon with 1.6 MeV helium at fluences ranging from 1 × 1016 to 1 × 1017 He/cm2 while keeping a constant dose rate. These samples were then subjected to 800°C annealing for 30 min. The results obtained by means of cross-sectional transmission electron microscopy indicate that the density of cavities is fluence dependent with homogeneous distribution of cavity sizes when fluences of 5 × 1016 and 1017 He/cm2 are used. The threshold fluence required to form cavities is found to be between 1 and 2 × 1016 He/cm2. For the 2 × 1016 He/cm2 dose, we observed loop punching induced by a concerted action of overpressurized bubbles, whereas He implants at doses of 5×1016 and 1×1017/cm2 lead to the formation of {311} defects. At the same time, non-Rutherford elastic backscattering (NREBS) experiments using 2.5 MeV H+ provide the fraction of helium remaining in cavities after different annealing times at 800°C. The NREBS data show a fast He release process for short annealing times (< 2000 s). Then, the He amount decreases slowly and after 30000 s about 40% of the helium still remain in cavities. Finally, an additional implantation with 50 keV He at 5 × 1016 He/cm2 shows the difference in cavity size distribution between MeV and keV implantation. © 2000 American Institute of Physics.