Low-voltage and ultra-low-voltage scanning electron microscopy of semiconductor surfaces and devices

Low-voltage scanning electron microscopy (LV-SEM) enables us to directly examine non-conducting materials with high spatial resolution. Although use of ultra-low-energy electrons can provide further advantages for characterizing delicate samples, lens aberrations rapidly deteriorates the image resolution. The combined use of a retarding field and the probe-forming lens system can improve the image resolution for electrons with very low energies. In commercially available FEG-SEMs, the retarding field can simply be constructed by applying a negative potential to the specimen. Interesting contrast variations have been observed in ultra-low-voltage SEM images. In this short communication, we discuss the application of LV-SEM to examining semiconductor devices and also the recent development of the ultra-low-voltage SEM technique.