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.

Comparison of arsenic diffusion in Si1−xGex formed by epitaxy and Ge+ implantation

“…Furthermore, Jones et al 11 reported that low-temperature amorphizing implants led to dislocation loops which did not hamper the flow of interstitials across the amorphous/crystalline interface. As the Si ϩ implant in our work was performed using liquid-nitrogen cooling, this mechanism could also contribute to increased arsenic diffusion in the Si ϩ implanted layers.…”

Interaction of interstitials with buried amorphous layer in silicon

“…They are elongated along <110> directions and lie in {311} planes and were therefore identified as {311} defects. These defects are known to be formed at the EOR after recrystallization of amorphous layer created by Si or Ge implantation [18,19]. In the case of Li implantation at liquid nitrogen temperature, they were not observed after annealing at 600 °C for 30 minutes [12].…”

Formation of Ultra-Shallow Junctions

“…Of the various choices for pre-amorphization species, Ge þ is the most promising amorphization agent (Jones et al, 1997) primarily because it is known to result in lower sheet resistance than either argon or fluorine (Colombeau et al, 2004). The advantage of Ge over Si is that the former is a heavier atom and therefore, a lower implantation dose is sufficient to create a uniform amorphous layer.…”