The production and use of ultralow energy ion beams

An ion accelerator, purpose built to produce beams at energies down to 10 eV with current densities in the 10-100 μA cm^-2 range, is described. Fitted with dual ion source assemblies, the machine enables ultralow energy ion implantation and the growth of films and multilayers to be carried out under highly controlled conditions. The accelerator delivers ion beams into an ultrahigh vacuum chamber, containing a temperature controlled target stage (range -120 to +1350°C), where they are used to study the fundamental physics relating to the interaction of ultralow energy ions with surfaces. This knowledge underlies a wide range of ion-beam and plasma-based technologies and, to illustrate its importance, results are presented from investigations designed to determine the optimum conditions for the growth of diamond-like and aluminum films by ion-beam deposition and the formation of ultrashallow junctions in semiconductors by 2.5 keV As⁺ implantation. The later investigation shows how transient arsenic diffusion, which occurs during post-implant thermal processing, can be controlled by manipulating the substrate temperature during implantation.