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 N
ss
energy 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 N
ss
shows good correlation with 1/f noise measurements, shows overlap of N
ss
values obtained at different temperatures and shows good correlation between measured Q
ss
values and those values calculated from the measured N
ss
profile. 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
^-17
cm
²
at 300°K to approximately 10
^-22
cm
²
at 77°K.