Electron-beam testing of VLSI circuits

The voltages at the internal voltage nodes of an IC have to be measured if the device operates imperfectly or the quality of a device or computer simulation have to be checked. Whereas the mechanical probe conventionally used for this purpose usually imposes such a large capacitive load on the specimen that its performance undergoes a change, the electron probe is both nonloading and nondestructive and can be used not only for quantitative waveform measurements on an IC but also for obtaining images of the logical states of relatively large portions of its circuit configuration. Since each type of configuration calls for a separate measuring technique, six different techniques are treated and their application and equipment needs described. The state of the art of electron-beam testing is demonstrated with reference to three typical applications, viz., checking a decoding schema, measuring the sense signal (approximately 300 mV) of a 16-kbit MOS RAM, and checking the operation of the timing circuitry of a 4-bit microprocessor. The present applicational limitations and future perspectives of electron-beam testing are discussed.