Properties of CeOx/La2O3 gate dielectric and its effects on the MOS transistor characteristics

Both n-channel and p-channel metal-oxide-semiconductor (MOS) transistors were fabricated by using CeOx/La2O3 stacked gate dielectric film and tungsten metal electrode. X-ray photoelectron spectroscopy (XPS) measurements indicated that the as-deposited CeO2 was reduced to CeOx (a mixture of CeO2 and Ce2O3 phases) and the released oxygen atoms filled up the oxygen vacancies in the La2O3 film and thus improved the electrical characteristics of the transistors. We found that the amount of the dielectric defects in this structure were very low as evidenced by the recorded small threshold voltages for both types of transistors. The transistors also have excellent subthreshold characteristics and hot-carrier robustness. The subthreshold slopes were 72 and 73 mV/dec for n-channel and p-channel transistors with effective gate length of 1.8 μm, respectively, and remain fairly unchanged upon prolonged hot-carrier stressing.