Effects of hydrogen on positive charges in gate oxides

Positive charge formation in gate oxides is a main source for the instability of the state-of-the-art metal-oxide-semiconductor device. Despite past efforts, the relation between hydrogenous species and positive charges is not fully understood. In this work, the effects of hydrogen on positive charges will be investigated at both elevated temperature (e.g., 400 degrees C) and room temperature. At 400 degrees C, it is found that hydrogen can convert some defects into hole traps. Three different types of positive charges have been reported recently. They are as-grown hole traps, anti-neutralization positive charges (ANPC), and cyclic positive charges (CPC). Although an exposure to hydrogen at 400 degrees C neutralizes all three, impacts of hydrogen on these three types of defects are markedly different. After the hydrogen-induced neutralization, the defect responsible for ANPC is fully recovered and is the same as that in a fresh device. In contrast, the defect for CPC is not fully recovered and can be reactivated easily by stresses. The as-grown hole trap can be converted to ANPC through hydrogenation. At room temperature, it will be shown that there are two parallel processes for forming positive charges. One involves hydrogen and the other is through hole trapping. The relative importance of these two depends on the relative density of hydrogen against that of holes. (C) 2005 American Institute of Physics.