抄録
Iron distribution in thin film oxide on silicon wafers is investigated in conjunction with the generation of a negative charge due to Fe in the oxide. The investigation uses the ac surface photovoltage (SPV) technique. Prior to thermal oxidation, Si wafers are treated with an Fe-contaminated alkaline solution composed of ammonium hydroxide, hydrogen peroxide, and water. During thermal oxidation, Fe atoms which are deliberately added to the wafer surface tend to segregate at the top of the oxide layer. This is confirmed by a sophisticated impurity-extraction technique combined with a high-resolution chemical analysis technique. For Fe-contaminated oxide films on n-type Si wafers, ac SPV appears, indicating that the negative charge due to Fe in the native oxide survives during thermal oxidation. The negative charge disappears after etching off the surface layer of the oxide to a depth of about 7 nm. In p-type Si, the negative charge compensates the positive fixed oxide charge localized at or near the SiO2–Si interface, resulting in the reduction of the ac SPV. The creation of the negative oxide charge is attributed to the replacement of quadrivalent Si ions by trivalent Fe ions in the oxide.
