Intrinsic low-field conduction in SIMOX buried oxides

Abstract

SOI technology is a prime candidate for replacing bulk Si in low-power VLSI CMOS applications. One of the most advanced SOI technologies is SIMOX. One potential problem with SIMOX SOI substrates is the intrinsic low-field conduction through the buried oxide (BOX), which is to be distinguished from defect-related "piping" current. Intrinsic low-level current, summed up over a very large chip area, could add up to a significant leakage component. In addition, low-level leakage poses a long-term reliability problem due to the potential for BOX charge trapping. Thus, a fundamental understanding of this low-field conduction is necessary in order to provide insight about the physical properties of the SIMOX BOX responsible for this current. In this paper, we present one of the first comprehensive studies of the electric-field, temperature, and time dependence of intrinsic low-level SIMOX BOX conduction characteristics for both single and multiple implant substrates. Based on the observed power-law time dependence, we believe that the low-level conduction is due to electron detrapping from pre-existing traps. The effect of Fowler-Nordheim (F-N) stress on low-field leakage is also examined. It was found that high-field stress can fill traps within the BOX which can then easily detrap at room temperature.