USING DOPING SUPERLATTICES TO STUDY TRANSIENT-ENHANCED DIFFUSION OF BORON IN REGROWN SILICON

A boron-doped silicon superlattice consisting of three boron spikes se parated by 1700 Angstrom of undoped silicon has been grown by molecula r beam epitaxy and used to study the evolution of point defects follow ing an amorphizing implant of Si+. After MBE growth, the wafer was imp lanted at 77 K with either 146 or 292 keV Si+ at a dose of 5x10(15)/cm (2). These implants produced amorphous layer depths that coincided wit h the depths of either the middle B peak or just below the deepest B p eak. The samples were then annealed at 800 degrees C in an Ar ambient. Secondary-ion-mass spectrometry and transmission electron microscopy were used to monitor the diffusion of the boron spikes upon annealing and the evolution of the extended defects upon annealing, respectively , For the lower-energy sample, an enhancement in the B diffusivity of over 500X was observed for both the surface B spike and the deepest B spike. The higher-energy implant shows conclusively that the back flow of interstitials into the regrown region is coming from the end-of-ra nge damage just below the amorphous/crystalline interface. These resul ts show that for these implant conditions the end-of-range damage does not act as a barrier to flow of interstitials to the surface. In addi tion it is noted that boron in the regrown silicon does not cluster wh ereas the boron below the amorphous crystalline interface does. Both o f these features must be accounted for when modeling boron diffusion i n regrown silicon. (C) 1996 American Institute of Physics.