A heavy negative ion sputter source: Production mechanism of negative ions and their applications

Abstract

Heavy negative ions can be produced by sputtering a metal surface at high efficiency by means of a secondary ion emission process. The most important factor for obtaining high negative ion production efficiencies is to maintain approximately one-half monolayer of Cs on the sputter target which produces a minimum in the surface work function. In a dynamic situation in which the surface is being bombarded by heavy ions, the cesium coverage is determined by a balance between the incoming and outgoing cesium fluxes. The supply of additional cesium to the surface and control of the target temperature are then essential for high negative ion production efficiency. The Neutral and Ionized Alkaline metal Bombardment type heavy Negative Ion Source (NIABNIS) in which a continuous negative ion current of a few hundred μA for several elements can be extracted, can be directly used for applications in materials science, such as negative ion beam deposition and negative ion implantation.