ELECTRICAL-ACTIVITY AND STRUCTURAL EVOLUTION CORRELATIONS IN LASER AND THERMALLY ANNEALED AS-IMPLANTED SI SPECIMENS

Laser-annealed and further thermally annealed arsenic implanted silicon specimens have been investigated in a range of doses from 1×10 16 to 5×1016 As/cm 2, with different experimental techniques: electrical measurements, transmission electron microscopy (TEM), double-crystal x-ray diffractometry (DCD), and extended x-ray absorption fine structure analysis (EXAFS). On the as laser-annealed samples, in the whole range of doses examined, a lattice contraction of the doped layer has been evidenced by DCD, whereas, on the same specimens, EXAFS measurements have shown the presence of a local expansion around substitutional As atoms. The relationship between strain and carrier concentration has been found to be approximately linear and can be described by the presence of a size and an electronic effect, as recently proposed in the literature. The former effect represents the atomic size contribution, while the latter is the strain induced by the variation of the conduction-band minima due to the doping. After a subsequent thermal annealing in a low-temperature range (350-550 °C), a strong deactivation of the dopant has been evidenced by electrical measurements. From the experimental results, a new model of the first step of the As deactivation phenomenon at low temperature is proposed. It is described by the capture of two electrons from a pair of As atoms in the second neighbor position in the Si lattice, leading to the formation of a positively charged arsenic-vacancy cluster (As2V)+, and to the emission of a negatively charged Si self-interstitial I-. This model takes into account the main phenomena that are experimentally observed simultaneously to the As deactivation, i.e., the transition from a contraction to a dilatation of the strain observed by DCD and the formation of interstitial loops. At relatively high temperatures (650-900 °C), the hypothesis of the coexistence of the clusters and of the observed precipitates has to be taken into account in order to explain the nature of the inactive As. However, whether clustering or precipitation is the dominant phenomenon still remains an open question.