Measurement of low defect densities in SIMOX using transmission electron microscopy

In order to reduce short channel effects for devices with channel lengths less than 0.25 μm, the buried oxide (BOX) thickness will need to be less than 200 nm. To this end, an experimental low dose (0.7×10¹⁸/cm²) oxygen implantation process for thin-BOX SIMOX has been explored. The extended defects in this material are predominantly dislocation pairs that run from the superficial Si/BOX interface to oxide precipitates. As in all electronic materials, the dislocation density in the device region must also be minimized. A reduction in the superficial Si layer dislocation density from ~10⁷/cm² to an estimated value of less than 100/cm² was achieved by subjecting this material to a prolonged (16 hour) anneal at 1325°C in an atmosphere of 0.5% O₂ in Ar. The anneal effectively reduced the device silicon layer from 270 nm to 200 nm as measured by cross-sectional transmission electron microscopy (TEM). The BOX layer thickness was unchanged by the anneal and remained at 130 nm