Characterization of flatband voltage roll-off and roll-up behavior in La₂O₃/silicate gate dielectric

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 La₂O ₃ 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.