An ion implantation process comprises performing mass separation of ions from an ionised source of phosphorous so as to select the P2 ions and reject phosphorous hydride ion species. The P2 ions are injected into a semiconductor substrate. The rejection of phosphorus hydride ions species is facilitated because there are no such species adjacent (in terms of effective mass) the P2 ion species. The use of the P2 ion species also improves the implantation process for shallow implantation depths.
