The utilization of charge pumping techniques to evaluate the energy and spatial distribution of interface states of an MOS transistor

The determination of both the energy and spatial distribution of interface states of an MOS transistor utilizing charge pumping measurements is described. In order to obtain an Nssenergy profile, charge pumping measurements must be made at several temperatures. The energy profile obtained shows several maxima and minima, but a gradual increase in magnitude as the band edge is approached. The measured energy dependence of Nssshows good correlation with 1/f noise measurements, shows overlap of Nssvalues obtained at different temperatures and shows good correlation between measured Qssvalues and those values calculated from the measured Nssprofile. The spatial distribution of interface states is determined by measuring the frequency dependence of the charge pumping current. The devices tested showed an exponentially decreasing interface state density away from the surface. Information is also obtained on capture cross-sections from the frequency dependence of the charge pumping current. Capture cross-sections are shown to decrease in value from approximately 10-17cm2at 300°K to approximately 10-22cm2at 77°K.