Voltage measurements on integrated circuits using the scanning electron microscope

The scanning electron microscope (s.e.m.) is widely used for the topographical examination and X-ray elemental analysis of integrated circuits, and is increasingly being used in electrical contrast modes. The voltage-contrast (v.c.) mode is particularly important because of the small dimensions of the devices found in current l.s.i. circuits which preclude the use of mechanical probes, and because of the minimal circuit loading which the electron beam imposes in high-frequency applications. Voltage contrast can now give a fair degree of measurement accuracy both in the static and dynamic cases. The dynamic situations often require the use of stroboscopic and sampling techniques, where the primary electron beam is chopped at a frequency locked to that of the signal being examined.