Ion-implantation issues in the formation of shallow junctions in germanium

This paper provides an overview of the current state-of-the-art in the formation of shallow junctions in germanium by ion implantation, covering the issues of dopant activation, diffusion and defect removal. As will be shown, for the case of p+ implantations, the application of rapid thermal annealing (RTA) to B implants yields good sheet resistance values, corresponding with activation levels well above the maximum solid solubility. A further improvement can be achieved by the use of a Ge pre-amorphization implant (PAI), which also removes the stable extended defects observed after high-dose B implantations. It will be shown that the formation of shallow n+ junctions is a more challenging field due to the rather low dopant solubilities and high diffusivities. However, encouraging results will be reported on the application of laser and flash-lamp annealing of P implantations in Ge. Also point-defect engineering is shown to be successful in controlling the junction formation.