Surface states at steam-grown silicon-silicon dioxide interfaces

A method of determining the energy distribution of surface states at silicon-silicon dioxide interfaces by using low-frequency differential capacitance measurements of MOS structures is described. Low-frequency measurements make it possible to determine the silicon surface potential as a function of MOS voltage directly from the experimental data without requiring knowledge of the Si doping profile. No graphical differentiations are required to determine the surface state density from the experimental curves, and errors introduced by uncertainties in the silicon doping density are reduced. Also, it is shown that the measurements can be used to determine the relative lateral uniformity in the characteristics of the oxide and interface under the MOS field plate. Nonuniformities can result in large errors in the surface-state density derived from MOS capacitance measurements. Measurements are presented and interpreted for both n- and p-type silicon samples prepared by bias-growing the oxide in steam.