Damage Assessment in Low Doses³⁰Si⁺-Implanted GaAs

Abstract

Ion implantation is a widely used technique in device technology, and becoming even more important as the size of devices decreases. The studies of damage and introduced defects have been extensive and, although the overall development and annealing of the implantation damage is relatively well understood, many details remain unclear. Especially, not enough attention has been paid to the effects of very low doses, which are particularly important in controlling the threshold voltage of transistors in the fabrication of GaAs integrated circuits. The reason might be that the induced changes were very often below the detectivity limits of standard methods. In this work, we present the disorder analysis, conducted on GaAs implanted with low ion doses. Czochralski grown, undoped, (100) oriented GaAs samples were implanted with 100 keV 30 Si + ions, doses ranging from 3 × 10 11 /cm 2-3 × 10 13 /cm 2 , at 21 • C. The damage assessment was done by applying Raman scattering and Rutherford backscattering ion channeling (RBS), linked by the inter-cascade distance model and the results were then compared with the results of photoacoustic displacement technique. We have shown that Raman scattering is very sensitive method even if applied on samples implanted with very low doses. Furthermore, the equivalency between the Raman scattering and Rutherford backscattering damage assessment, previously established for high doses via the inter-cascade distance model, proved equally valid also for very low implantation doses, where implanted ions create disordered cascades that are far apart, and most of the layer is still undamaged.