Fixed oxide charge in n-type silicon wafers studied by ac surface photovoltage technique

A fixed oxide charge (Q(f)) in n-type silicon (Si) wafers is investigated in thermally oxidized Si wafers intentionally contaminated with aluminium (Al), where Al-induced negative charge clarified by an ac surface photovoltage plays the role of a charge marker. Q(f), which is defined to be positive, in n-type Si wafers is found to be almost completely neutralized by abundant majority carriers (electrons in n-type Si) during thermal oxidation at high temperature. Consequently, the positive oxide charge might disappear in n-type Si wafers. Instead, the resultant oxide charge in thermally oxidized n-type Si wafers is often negative because of possible interface-trapped charge.