Use of a duoplasmatron ion source for negative ion generation

Abstract

The use of electronegative species as primary ions considerably enhances the emission of positive secondary ions in SIMS. Considering furthermore that negative primary ions can be required due to instrumental configurations (e.g. the Cameca NanoSIMS 50 requires an opposite polarity of the primary and secondary ions), O − ion bombardment is employed in SIMS analysis. These O − ions are typically created in a duoplasmatron source, which suffers however from its low brightness and which is thus not suited for high resolution imaging applications. The development of new (electro)negative ion sources is thus necessary to optimize the analysis of electropositive elements in terms of lateral resolution and sensitivity. In this paper, we present the performance of a duoplasmatron ion source generating F −, Cl −, Br − and I − ion beams. In particular, we experimentally determine on a dedicated test bench the brightness of the source in the F −, Cl −, Br − and I − modes as a function of the gas pressure, the magnetic field strength and the arc current in the source. The obtained results are compared to the performances of the duoplasmatron in the standard O − mode. In this context, a five times higher brightness was found for F − (200 A/cm 2 sr) compared to the standard O − (42 A/cm 2 sr).