Diffusion of ion implanted boron in preamorphized silicon

Abstract

Transient enhanced diffusion of boron in preamorphized and subsequently regrown Si was studied by secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM). A comparison of 4 keV, 1× 1014/cm2 boron implants into crystalline and Ge+ preamorphized silicon was undertaken. Upon annealing the B+ implant into crystalline material exhibited the well-known transient enhanced diffusion (TED). In this case the peak of the boron distribution was relatively immobile and only B in the tail showed TED. In the second set of samples, the surface was first preamorphized by a 180 keV, 1×1015/cm2 Ge+ implant which produced an amorphous layer 2300 Å deep, which then was implanted with boron. After implantation the tail of the B distribution extended to only 700 Å. Upon annealing, TED of the boron in the regrown Si was also observed, but the diffusion profile was very different. In this case the peak showed no clustering, so the entire profile diffused. The time for the TED to decay was around 15 min at 800 °C. TEM results indicate that the (311) defects in the end of range damage finish dissolving between 10 and 60 min at 800 °C. These results indicate that for these Ge preamorphization conditions, not only do the end of range defects not block the flow of interstitials into the regrown silicon, the (311) defects in the end of range damage act as the source of interstitials. In addition, boron does not appear to cluster in regrown silicon.