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 x 10(16) to 1 x 10(17) He/cm(2) while keeping a constant dose rate. These samples were then subjected to 800 degrees 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 x 10(16) and 10(17) He/cm(2) are used. The threshold fluence required to form cavities is found to be between 1 and 2 x 10(16) He/cm(2). For the 2 x 10(16) He/cm(2) dose, we observed loop punching induced by a concerted action of overpressurized bubbles, whereas He implants at doses of 5 x 10(16) and 1 x 10(17)/cm(2) 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 degrees C. The NREBS data show a fast He release process for short annealing times (< 2000 s). Then, the He amount decreases slowly and after 30 000 s about 40% of the helium still remain in cavities. Finally, an additional implantation with 50 keV He at 5 x 10(16) He/cm(2) shows the difference in cavity size distribution between MeV and keV implantation. (C) 2000 American Institute of Physics. [S0021-8979(00)02304-5].