Effect of a field-limiting method in a micro-area analysis by SIMS.

Regarding micro-area analysis by means of scanning SIMS (micro-probe mode), the effect of the primary ion-beam size and its spreading tail causes some problems, which usually lead to a degradation of the spatial resolution of the analysis and, more directly, to a worse detection limit for some impurities. We investigated the usefulness of the field-limiting method in order to improve the detection limit in a micro-area SIMS analysis using a CAMECA IMS-4f type apparatus, which is capable of both microscope and microprobe measurements. By evaluating the detected background level of (P+30Si)- from a P-implanted Si sample, it was confirmed that the field-limiting method improves the detection limit of this ion species by a factor of ten. This might be achieved by a elimination of the interfering ions (29Si16O2)- ejected from the outskirts of the rastering area of the primary ion-beam.