A review of positive charge formation in gate oxides

Positive charge formation in gate oxides is an important reliability issue for CMOS technologies. Despite of the efforts in the last several decades, our understanding of it is still limited. In this paper, recent progresses in this area are reviewed. We start with as-grown hole traps and then demonstrate that new hole traps can be created by electrical stresses. Properties of both generated and as-grown hole traps are investigated and compared. Different types of hole traps are identified and the relation between hole traps and the well-known anomalous positive charges were explored. Finally, we show that, apart from hole trapping, positive charges can also be formed by creating nonreactive hydrogenous species.