This invention relates to a scanning electron microscope, and particularly to an electron beam scanning method and a scanning electron microscope suitable for the observation and measurement of the shape of insulation samples.
For the observation of the shape of an electrical insulation sample with a scanning electron microscope (SEM), the electron beam acceleration voltage is desirably selected to a lower voltage, e.g., around 1000 volts, in order to reduce charges on the sample. However, when a sample of various insulation materials undergoes a sequential linear scanning with an electron beam, it has slightly different charged voltages at the starting and and ending portions of scanning even if the sample is symmetric in shape with respect to the horizontal direction, resulting in a slightly asymmetric waveform of the secondary electron output signal.
Although the above-mentioned conventional method is suited to determine the approximate shape of a sample by observation, the asymmetry of the output signal waveform imposes a problem when the shape of sample is observed more accurately, a specific portion of the sample shape is recognized accurately from the waveform of secondary electron output signal, or the dimensions of a specific portion of a sample is measured.