Positive charge trapping in SOI materials

It is well known that unwanted charge in the Silicon-On-Insulator (SOI) buried-oxide (BOX) can adversely affect integrated circuit (IC) yield (back-gate threshold location), IC performance (controlling vertical isolation), and IC reliability (hot electron effects). Although previous studies have shown that the concentration of electron traps in the Separation-by-IMpIanatation-of-OXygen (SIMOX) BOX depends on the conditions used to fabricate the SIMOX wafer, there has been little success in reducing positive charge trapping in the BOX, which is predominantly from hole trapping. In this work we report our measurements of X-ray induced positive charge trapping in the BOX of wafers fabricated using various SOI technologies, and in bulk thermal oxides. We find that for similar oxide thicknesses the SOI material has a trapping sensitivity 10 to 100 times larger than thermal oxides. We also find that annealing finished SIMOX wafers in oxygen appears to successfully reduce some positive charge trapping in the BOX