Experimental verification of buried-oxide with over-8 MV/cm breakdown fields in low-dose SIMOX wafers

Low-dose SIMOX wafers have attractive features as the material for advanced commercial CMOS LSIs, such as lower cost, and lower threading dislocation density (/spl sim/10/sup 2/ cm/sup -2/) than high-dose SIMOX. However, the low-dose SIMOX wafers prepared by the Internal-Thermal-OXidation (ITOX) process, still exhibited lower breakdown fields (E/sub BD/s) for the buried-oxide (/spl sim/5.5 MV/cm), when compared to the intrinsic E/sub BD/ of the thermal-oxide (>8 MV/cm) at Si surface in most cases. It has been pointed out that the E/sub BD/ degradation of Buried-OXide (BOX) is caused by the presence of Si islands in the BOX. We report here that BOX E/sub BD/s for the low-dose SIMOX is upgraded from the level of the previous case to that of thermal oxide (>8 MV/cm) by the reduction of Si islands and becomes more practical to larger unit-device-size area (7.85/spl times/10/sup -3/cm/sup 2/).