The roll-off and roll-up behavior of flatband voltage (V-fb) on equivalent oxide thickness (EOT) of La2O3/silicate capacitors have been characterized by X-ray photoelectron spectroscopy and modeled by the fixed charges. It has been revealed that the thickness of the reactively formed silicate layer is dependent on the La2O3 thickness initially deposited on the wafer. When the La2O3 thickness is over 3 nm, the silicate layer has been found to be formed with a constant thickness of 1.6 nm. However, while decreasing the La2O3 thickness to 1 nm, the thickness of silicate layer decreases due to the reduction of radical oxygen atoms originated from the La2O3 layer, resulting in the formation of La-rich silicate. The V-fb roll-off behavior can be attributed to the enhanced generation of positive fixed charges induced by the diffusion of metal atoms from the gate electrode into the silicate layer. On the other hand, the V-fb roll-up behavior can be explained when the initially deposited La2O3 layer has been all converted into silicate. (C) 2010 Elsevier Ltd. All rights reserved.