DIFFUSION OF DOPANTS IN B-DELTA-DOPED AND SB-DELTA-DOPED SI FILMS GROWN BY SOLID-PHASE EPITAXY

The diffusion of delta-function-shaped B- and Sb-dopant spikes in thin Si films grown by solid-phase-epitaxy [(SPE), growth of amorphous fil m by molecular-beam epitaxy (MBE) at room temperature and subsequent r egrowth in situ] during annealing in vacuum is compared to diffusion i n films grown by low-temperature (LT) MBE. Diffusion temperatures from 750 to 900-degrees-C, and two-dimensional concentrations of 0.7-1.6 X 10(14) cm-2 have been investigated. The diffusive behavior of dopants in SPE films is found to be qualitatively different from that in film s grown by LTMBE. This is related to the vacancylike defects that are intrinsic to growth by SPE but not to growth by LTMBE. Dopant profiles widen significantly during SPE regrowth, making the achievement of de lta-function dopant spikes impossible. After a vacuum anneal the diffu sion coefficients for both n- and p-type dopants are lower in SPE film s than the corresponding values in films grown by LTMBE by up to one o rder of magnitude. The diffused depth profile of the dopant in LTMBE f ilms shows the characteristic deviation from a pure Gaussian that is e xpected due to the concentration dependence of diffusion, i.e., a flat top and steep shoulders. In contrast, dopant depth profiles of SPE-gr own material show after diffusion a central spike and relatively flat shoulders. The width of the central spike is, after an initial transie nt that it was not possible to resolve, independent of diffusion time and temperature. This indicates that the SPE material is defective, wi th the defects acting as traps during diffusion.