Effects of Segregated Ge on Electrical Properties of SiO2/SiGe Interface

The effects of segregated Ge on the electrical properties of the SiO2/SiGe interface are investigated. It is observed that the segregated Ge near the SiO2/SiGe interface, formed during oxidation of the SiGe layer, affects the threshold voltage of a metal-oxide-semiconductor (MOS) structure, and that the flat-band voltage shift increases when the Ge segregation is increased. The densities of the interface states and fixed charges are measured using the capacitance-voltage (C–V) method, and the relationships between these results and the material properties are examined. From the results, the SiO x structures are responsible for the increased negative fixed charges near the SiO2/SiGe interface. The mechanism proposed for the generation of negative fixed charges is that the oxygen in the Ge pileup region forms a Si–O–Ge bonding structure initially, and then the weaker Ge-O bond can easily be broken, leaving a Si–O– dangling bond and elemental Ge. The Si–O– dangling bond assumes a negative fixed charge state by trapping an electron.