Strategies for Low Accelerating Voltage X-ray Microanalysis of Sub-Micrometer Features with the FE-EPMA

X-ray microanalyses of sub-micrometer features require that a lower accelerating voltage be used. This reduction in the accelerating voltage reduces the penetrating distance of the beam electrons and thereby reduces the analytical volume. Two general strategies have been proposed for achieving the smallest analytical volume. The first approach involves significantly reducing the accelerating voltage to minimize the electron interaction volume. For many element systems, the optimum accelerating voltage is in the 5-8kV range, assuming a field emission electron gun is used for the analysis. A lower kV will reduce the penetrating depth of the electrons further. However with lower kV, the diameter of the electron beam becomes a critical factor in determining the analytical area, and with a lower kV, the beam diameter becomes larger. Mostly this comes from the higher required beam current used due to the lower X-ray production rate at the lower kV. This low-kV strategy also typically requires a different set of X-ray lines be used, since some of the more commonly used X-ray lines are not generated at these lower accelerating voltages. However, it can produce a very small analytical volume (Fig. 1a).