Mechanisms of dopant redistribution and retention in Silicon following ultra-low energy boron implantation and excimer laser annealing

Excimer laser annealing (ELA) of ultra-low energy (ULE) B ion implanted Si has been studied and the process has been shown to allow for the formation of ultra-shallow junctions (35nm) with abrupt profiles (2.5 nm/decade), applicable to the future requirements of semiconductor devices. High resolution transmission electron microscopy has been used to assess the as-implanted damage and the crystal recovery following ELA. The electrical activation of B in Si during ELA has been investigated as a function of laser energy density (melt depth), implantation energy and number of laser pulses (melt time). The activated and retained does has been evaluated with spreading resitance profiling and secondary ion mass spectrometry. A significant amount of the implanted dopant was not activated following ELA. The fraction of the implanted dopant which was not activated during ELA was lost from the sample through out diffusion. However, the dopant that was retained in crystal material during ELA was fully activated and no defect regions have been observed at the surface and at the liquid-crystal interface position. The electrical activation was increased for high laser energy density annealing when the dopant was redistributed over a deeper range.