Transient enhanced diffusion and defect microstructure in high dose, low energy As+ implanted Si

(001) CZ silicon wafers were implanted with As+ at 100 keV to a dose of 1 X 10(15)/cm(2) in order to produce a continuous amorphous layer to a depth of about 120 nm. Furthermore, the implant condition was such that the peak arsenic concentration was below the arsenic clustering threshold. Subsequently, a second As+ or Ge+ implant was performed at 30 keV to doses of 2 X 10(15)/cm(2), 5 X 10(15)/cm(2) and 1 X 10(16)/cm(2), respectively, into the as-implanted samples. All of the samples were annealed at 800 degrees C for 1 h. The second implant was designed to be contained within the amorphous region created by the initial implant. The second As 1 implant was also designed to provide the additional arsenic needed to exceed the critical concentration for clustering at the projected range. Of the three samples with the dual As+ implant the clustering threshold was exceeded for the two lower doses while the SiAs precipitation threshold was exceeded at the highest dose. In the case of the dual As+/Ge+ implants the clustering and precipitation thresholds were not reached. Since arsenic and germanium are similar in mass the extent of damage created by these implants would be comparable. The implanted and annealed specimens were analyzed using secondary ion mass spectroscopy and transmission electron microscopy. The difference in the defect evolution and the transient-enhanced diffusion of arsenic beyond the end-of-range region between the As 1 and Ge 1 implanted and annealed samples was used to isolate the effects of arsenic clustering and precipitation. The results showed that point defects induced during clustering and/or precipitation did not contribute to the enhanced diffusion of arsenic although these defects did coalesce to form extended defects at the projected range. However, damage beyond the end-of-range region did cause enhanced diffusion of arsenic. (C) 1998 American Institute of Physics. [S0021-8979(98)05923-4]