Defect and bulk electrical conduction in SIMOX buried oxides

The authors examine the current-voltage characteristics of SIMOX (separation by implanted oxygen) buried oxides through measurement of buried-oxide MOS capacitors built by doping the superficial silicon heavily n- or p-type and patterning it into electrodes varying in area from 0.00005 to 0.2 cm/sup 2/. Aluminum contacts are sometimes applied to the top surface to enhance probe contact. The level of conductivity is found to vary as much as nine orders of magnitude among capacitors on the same wafer; furthermore, there is no direct relationship between conduction level and sample area. This strongly suggests that localized defects are contributing significantly to the conductivity. Models for two types of defect-oriented conduction characteristics are shown. The type I defect which displays high conductivity at low bias is envisioned as a continuous filament or 'pipe' through the buried oxide, while the type II defect is seen as a similar structure that is discontinuous at some point in the oxide. Blowout of these structures leaves a large hole, which may or may not refill with fused silicon to impart a post-failure level of conduction.<
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