ION-INDUCED DAMAGE AND AMORPHIZATION IN SI

Ion-induced damage growth in high-energy, self-ion irradiated Si was studied using electron microscopy and Rutherford backscattering spectrometry. The results show that there is a marked variation in the rate of damage growth, as well as the damage morphology, along the path of the ion. Near the ion end-of-range (eor), damage increases monotonically with ion fluence until a buried amorphous layer is formed, while damage growth saturates at a low level in the region ahead. Damage growth remains saturated ahead of the eor until expansion of the buried amorphous layer encroaches into the region. The morphology of the damage in the saturated region is shown to consist predominantly of simple defect clusters such as the divacancy. A homogeneous nucleation and growth model, presented to account for damage saturation, is shown to also predict the dose-rate dependence of the saturation level. Mechanisms are identified which contribute to the unconstrained damage growth observed near the eor prior to amorphization, and subsequently at the interface of the buried amorphous layer. The effects of an imbalance in the generation rates of interstitials and vacancies on damage growth in the eor region are discussed. This imbalance is shown to arise either as a result of added atoms during implantation or spatial separation of the Frenkel defect pairs created during ion impact. A local, uniaxial strain field in the interfacial region of the amorphous layer is identified, and the possibility of its contribution to growth at that location is discussed.