LOW-VOLTAGE SCANNING ELECTRON-MICROSCOPY - A SURFACE SENSITIVE TECHNIQUE

The advancements in electron optics have made it possible to cover a wide electron energy range without significant degradation in the imaging quality of a scanning electron microscope. The secondary electron emission and the surface sensitivity are enhanced when using low voltages. The addition of an energy dispersive x-ray spectrometer with a thin window allows the detection of low energy emission lines, thus making the technique comparable, or at least complementary to surface techniques such as Auger electron and x-ray photoelectron spectroscopies. In this paper, aspects of low-voltage SEM are discussed and factors affecting the secondary electron images are examined. The surface sensitivity is evaluated and is compared to Auger electron spectroscopy. Study cases from the printed circuit board manufacturing area are presented.