Confirmation of Aluminum-Induced Negative Charge in Thermally Oxidized Silicon Wafers Using AC Surface Photovoltage Method

Abstract

The ac surface photovoltage (SPV) technique is applied for detecting the polarity of charge in thermally-oxidized silicon (Si) wafers, in which aluminum (Al) is deliberately incorporated in the native oxide. Upon thermal oxidation, most of the Al is contained in the oxide and it segregates at the very top of the oxide layer. With the increase of Al concentration in the oxide, ac SPV appears and increases for oxidized n-type Si wafers, whereas in p-type Si it decreases, indicating that Al acts as a negative charge by forming the (AlOSi)- network and compensates the positive fixed oxide charge. With the removal of the surface layer, for n-type Si, ac SPV disappears, whereas for p-type Si, it appears because the net positive fixed oxide charge becomes dominant.