ANOMALOUS DISTRIBUTION OF AS DURING IMPLANTATION IN SILICON UNDER SELF-ANNEALING CONDITIONS

Anomalous distribution of As implanted in silicon under self-annealing conditions (i.e., with simultaneous damage recovery activated by beam heating) has been investigated and discussed. Rutherford backscattering/channeling, transmission electron microscopy, and carrier profiling techniques have been used to analyze the dopant profiles and the microstructure of samples irradiated with 150-keV As+ ions at a current density of ?207 ?A/cm2, for times of 2, 3, 4, 5, and 6 s. Two relevant effects are observed. The first one consists in the formation of two dopant peaks, electrically inactive, separated by a depletion region at the position of the ion projected range. While the deeper peak disappears with increasing irradiation time, the one located at the maximum of nuclear energy loss grows. Microstructural analysis suggests that both peaks occur as a result of As segregation at lattice defects; in particular, the one located the position of the maximum of nuclear energy loss is the consequence of segregation of As atoms at voids, which are formed during irradiation at elevated temperature. The second relevant effect is the formation of a deep penetrating tail in the As profile, which cannot be explained by a simple thermal diffusion mechanism. Although the contribution of channeling effects cannot be ruled out, the effect seems to be mainly related to a diffusivity enhancement, weakly temperature dependent, due to the interaction of the dopant with radiation-induced defects.