An EXAFS investigation of arsenic shallow implant activation in silicon after laser sub-melt annealing

摘要

It is well known that arsenic deactivates easily in silicon at moderate temperature (500-800 ℃), supposedly by clustering around vacancies. The deactivation hinders the preservation of the high level of activation reached by processes such as solid phase epitaxial regrowth (SPER) or laser sub-melt annealing. This paper presents results obtained on 2 keV arsenic implants in silicon subsequently annealed by either laser sub-melt or spike processes. In particular, we investigated the local order around arsenic atoms by extended X-ray absorption fine structure (EXAFS) measurements. A sample preparation consisting of removal of some atomic layers was carried out to eliminate inactive dopant segregated at the surface oxide. The chemical depth profiles were measured by secondary ion mass spec-trometry (SIMS) whereas the electrical activation was investigated by four point probe and Hall effect measurements. The EXAFS results show that the spike annealing produces a surface accumulation with a local order around As atoms similar to the amorphous structure observed in the as implanted sample. After removal of the surface accumulation, EXAFS spectra are typical of a sample with a high level of activation. This was also observed for samples processed with laser sub-melt annealing before the spike anneal. Samples treated with the only laser process show an intermediate level of crystal order. Electrical data are in agreement with the qualitative EXAFS observations.