Formation of Subthreshold Defects in Erbium Implanted Silicon

ABSTRACTIn this work we present the first quantitative approach to model subthreshold defects. Using cross-sectional Transmission Electron Microscopy (XTEM) and Convergent Beam Electron Diffraction (CBED), we studied subthreshold defects in Cz-silicon that followed a deep implantation of erbium, and their interaction with co-implantations. The analyzed Frank loops show an increasing size by a factor of five with increasing depth in the wafer. The ratios of the number of condensed silicon atoms to the implant doses support a “+0.4 model” for the erbium and a “+0.07 model” for the oxygen as a co-implant. Our results indicate that a “push away” mechanism produces the excess silicon atoms in the case of interstitial implant atoms. The observed loop size depth distributions helped to reveal the condensation mechanism of subthreshold defects. This mechanism is described by the relaxation of excess silicon atoms on primary defect clusters. The decreasing concentration profiles of the primary defect clusters together with the high diffusivity of silicon interstitials results in a number of condensed silicon atoms per loop that increases with the depth in the wafer.