Ion Beam Analysis

Originally the advent of microelectronics gave rise to the need for rapid and accurate analysis of thin film structures. Generally, these planar structures were formed in silicon or germanium by either energetic ion implantation of dopants to create electrically active regions and/or by thermal reactions between thin metal films which were deposited onto them. Ion-beam modification (e.g., ion implantation) was a new technique in the early sixties, and interactions between metal films and silicon required analysis. For example, the number of ions implanted per square centimeter (ion dose) and the thicknesses of metal layers required careful control to meet the specifications of integrated circuit technology. Rutherford backscattering spectrometry (RBS) and MeV ion-beam analyses were developed in response to the needs of the microelectronics and forensic disciplines. In turn, integrated circuit technology provided the electronic sophistication used in the instrumentation in ion-beam analysis. It was a synergistic development of analytical tools and the fabrication of integrated circuits. Rutherford backscattering analysis is the measurement of the energies of ions scattered back from the surface and near the surface, the outer micron, of a sample. Figure 1 shows a depiction of a general ion-scattering chamber where samples are typically analyzed. Monoenergetic helium ions or protons with energies ranging from 1 to 5 MeV are used to analyze thin film materials ranging from integrated circuits to biomedical materials. Only moderate vacuum levels (~10^–6 torr) are required so that sample exchange is rapid; it allows the analysis to be done in a relatively brief....