A metrological electron microscope system for microfeatures of very large scale integrated circuits

An absolute linewidth measuring system, based on a scanning electron microscope (SEM), is developed to measure critical dimension (CD) of VLSIs (very large scale integrated circuits). The system employs two laser interferometers for the absolute scales of the X and Y axes, while the electron beam is used to detect microfeatures on the silicon chips. The resolutions of the interferometers are 0.8 nm for X and 20 nm for Y. An LaB6 filament is used for the electron gun and the system is operated under low acceleration voltages of around 1 kV for noncharging measurements. In this article, the principle of the measurements, the electron beam system, the scanning mechanism, and the laser interferometer are described including basic experimental results.