Quantitative secondary electron energy filtering in a scanning electron microscope and its applications

Two-dimensional dopant mapping in the scanning electron microscope (SEM) has recently attracted attention due to its ability to measure dopant levels rapidly with high spatial resolution while requiring little or no sample preparation. The dopant concentration could be derived from the energy distribution of secondary electrons emitted per doped region. However, the lack of reliable quantification, when standard SEM imaging is used, has so far hindered a wide application of the technique. This paper aims to resolve this problem with quantitative energy-filtering using a through-the-lens (TTL) detector in a field emission gun SEM (FEG-SEM). We have used the linear shift obtained in the SE energy distribution with variable specimen bias using sample containing copper wires, defined as the experimental detector response Rexp, to quantify the energy filtering. Using different experimental conditions, values of (2.42±0.04)⩽Rexp⩽(3.01±0.05) were obtained. Results were validated by comparison with calculations obtained from ray-tracing simulations. Recommendations for the linear range of the TTL detector as an energy filter were established on the basis of these results. In addition, using our quantitative energy-filtering capabilities, the potential difference across a Si pn-junction was measured to be 0.81±0.10 V, which is in good agreement with the calculated value.