Application of Low Voltage Scanning Electron Microscopy and Energy Dispersive X-Ray Spectroscopy

The application of field emission sources in scanning electron microscopy has resulted in significant improvements in spatial resolution, especially at low, <5kV, accelerating voltages. Low voltage operation has the advantage of reducing the interaction volume within the specimen, thus increasing the surface specificity of the technique [1, 2]. By working at the second crossover energy it is possible to neutralize the surface charge build-up at the surface of non-conducting specimens [3]. Theoretical and experimental methods for determining the optimum accelerating voltage will be described. Due to the reduced interaction volume, the contrast mechanisms may differ from those in the higher voltage range, >15kV, more generally used for scanning electron microscopy. Differential charging may strongly influence the local secondary electron yield, giving rise to anomalous atomic number contrast [4, 5]. The use of Monte Carlo modelling for image simulation and estimation of the size of the interaction volume will be illustrated with practical examples related to semiconductor critical dimension measurement and multilayer thin film studies.