Si film electrical characterization in SOI substrates by the HgFET technique

Abstract

A mercury-based "pseudo-MOSFET" is described which can be used to measure many electrical properties of the Si film in silicon-on-insulator (SOI) substrates, including the electron and hole mobilities, flat band and threshold voltages, BOX charge, interface state density, drive currents, output conductance, transconductances, and doping levels. In the HgFET, the source and drain are made by Hg electrodes on the Si film and the buried oxide/substrate forms the gate. An HF surface treatment is used which temporarily passivates the Si surface and deposits a short-lived ionic charge. Measurements are made over time as this charge dissipates and the surface state density increases. Comparisons with evaporated metal "ringFETS" and FETs made with Hall bars show that the same electrical parameters are obtained with all three devices. Data are shown for over 200 SOI wafer lots with Si layer thicknesses from 55 to 200 nm. Estimates are given for the accuracy of the different electrical parameters. © 2003 Elsevier Science Ltd. All rights reserved.