Hot electron effects in silicon-on-insulator MOSFETs fabricated by epitaxial lateral overgrowth
Abstract
The electronics industry continues to demand faster, denser integrated circuits. As device dimensions shrink short channel and hot electron effects become increasingly important, Silicon-on-Insulator (SOI) MOSFETs are attractive for high speed, high density integrated circuits. Dielectric isolation allows denser packing and reduced parasitic capacitances which allows for faster chips. For a given geometry an SOI device has lower electric fields and lower hot electron generation than a bulk MOSFET. However tests with SOI devices fabricated on SIMOX substrates have shown that fully depleted SOI MOSFETs degrade more rapidly under hot electron stress than do bulk devices. This is due to the presence of the second Silicon-Silicon dioxide interface in the SOI device and to the poor quality of the oxide layer formed by oxygen implantation. I have investigated the hot electron resistance of SOI devices fabricated by epitaxial lateral overgrowth (ELO). In this method the buried oxide is a normal thermal oxide with silicon grown epitaxially over the oxide. I have investigated the effect of the length of time that the was oxide was exposed to the epitaxial growth environment. I found that the oxide was thinned enough during epitaxy to effect the threshold voltage and the transistor's resistance to hot electron damage. The measured increase in degradation was approximately the amount predicted by the lucky electron model for the oxide thinning. I have measured the distribution of hot electron gate current and device degradation between the two channels. For P-channel devices with both channels conducting the gate currents is proportional to the channel current. When only one channel is conducting the gate current in the opposite channel is determined by the silicon thickness and the oxide electric field. For thin symmetric devices the opposite channel degradation can be larger than the conducting channel.
Degree
Ph.D.
Advisors
Neudeck, Purdue University.
Subject Area
Electrical engineering
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