The atomic site of as implanted in Si at ultra-low energies

The fabrication of ultrashallow junctions needs the realization of surface layers with a noticeably high (?10 21atoms/cm 2 ) dopant density. In the case of As doped Si, thermal treatments lead to changes in the atomic environment of the dopant and, thus, to its electrical activity. In this contribution the local order around As dopants in low energy (1 keV) implanted crystalline Si was studied by extended X-ray absorption fine structure. Data were collected in total reflection condition in order to enhance the signal from the surface. The quantitative analysis revealed a site for As that is different from the pure substitutional one and suggests the presence of clusters of As atoms coupled to vacancies.