Effect of implant temperature on transient enhanced diffusion of boron in regrown silicon after amorphization by Si+ or Ge+ implantation

Abstract

Si wafers were preamorphized by either Si+ or Ge+ ions at temperatures between 5 and 40 °C. The diffusion of low energy (4 keV) B+ implants into the preamorphized Si was studied in order to monitor the flux of interstitials from the end of range (EOR) region toward the surface. Transient enhanced diffusion (TED) in the regrown silicon was observed for all implants. Increasing the implantation temperature of the Si+ implant by as little as 15 °C can result in a marked decrease in the magnitude of the interstitial flux flowing from the EOR region toward the surface. This sensitivity to implant temperature appears to be even greater for Ge+ implants. In order to better understand this effect, detailed transmission electron microscopy (TEM) studies were conducted. As-implanted cross-sectional TEM micrographs indicate a measurable decrease in the thickness of the amorphous layer (up to 300 Å) occurs when the implantation temperature increases from 5 to 40 °C as a result of ion beam induced epitaxial recrystallization. Upon 800 °C annealing, two types of defects are observed in the EOR region: {311} defects and dislocation loops. The {311} defects are unstable and the comparison of secondary ion mass spectroscopy and TEM data for annealed samples indicating the dissolution of these {311} defects is at least one of the sources of interstitials for TED in the regrown Si at 800 °C. The EOR dislocation loops are stable for the annealing conditions used in this study (800 °C for 15 min) and there appears to be an exponential dependence of the TED that occurs in regrown Si on the density of the EOR dislocation loops.