Aluminum Oxide/Silicon Dioxide, Double-Insulator, MOS Structure

Aluminum Oxide/Silicon Dioxide, DoubleInsulator, MOS Structure By J. T. CLEMENS, E. F. LABUDA, and C. N. BERGLUND ( M a n u s c r i p t r e c e i v e d M a y 15, 1974) A double-insulator structure consisting of 500 A of vapor-deposited AlzOz and 1000 A of thermally grown SiO2 is used as the gate dielectric in a beam-lead-compatible, p-channel, MOSFET, silicon-integrated-circuit technology. The AI2O3 layer, in addition to serving as a sodium barrier and thereby providing a self-passivatecl technology, results in a positive flatband voltage shift when compared to an SiOz structure. The mechanism for this flatband voltage shift is the subject of this paper. The major experimental results obtained are (i) a negative charge exists near the AhOz/SiOi interface, its magnitude being independent of the AI2O3 thickness but inversely proportional to the SiO2 thickness, (ii) the magnitude of the Si02/Si interface charge is inversely proportional to the SiO2 thickness, and (Hi) a poten tial jump of about 1.25 volts in flatband voltage is associated with the addition of the AI2O3 layer. A physical model is proposed which assumes the existence of a constant voltage drop across the SiOo layer during the AI2O3 deposition and a corresponding charge buildup at the Si02/Al203 interface.