Dose-dependent precipitate evolution arising during implantation of Er into Si

Abstract

Implant dose effects arising from the implantation of Er+166 into Si(111) have been investigated. This study encompasses a wide dose range from 4×1015 to 1.2×1017at.cm−2 and focuses on channeled implantation as random implantation leads to a high degree of self-sputtering and damage in the resultant silicide precipitates. Dramatic changes are observed in the shape of the implant profile as a function of dose. Buildup of damage to the crystalline lattice and increasing target density as the implant proceeds lead to a piling up of subsequently implanted Er. Concurrently, sputtering and redistribution of the implanted species cause the implant profile to broaden. The crystalline quality and elastic strain of the resulting ErSi1.7 precipitates have been studied using Rutherford backscattering and channeling spectrometry and high-resolution x-ray diffraction. Following implantation, the precipitates are under compressive elastic strain perpendicular to the sample surface. Its magnitude increases linearly with dose and is attributed to the accumulation of irradiation-induced defects. A two-step improvement in crystalline quality is ascribed to the rapidly improving coherence of the growing precipitates with the Si lattice, succeeded by a slow improvement as the peak Er concentration approaches the silicide stoichiometry. Transmission electron microscopy imaging reveals that the transition between the two regimes corresponds to the formation of a continuous silicide layer. These results have consequences for both precipitate and layer formation using ion implantation.