Analysis of the local field effects on voltage measurements with an 'in-lens spectrometer'

Voltage measurements in integrated circuits are often performed with an electron probe, in which case the measurement accuracy is limited by the so-called 'local field effects' (LFE). By performing ray tracing for the secondary electrons, the sensitivity of 'in-lens detection' to LFE has been analysed. A promising mode of operation was found for low extraction-field strengths (e.g. 40 V mm-1). By combining such an extraction field with a suitable objective-lens field the most crucial measurement error resulting from the LFE can be compensated. This method can also be applied, at least in principle, for the inspection of submicrometre devices. The results are compared with experimental measurements, some differences are discussed in detail.