ERROR ANALYSIS OF SURFACE STATE DENSITY DETERMINATION USING MOS CAPACITANCE METHOD

A detailed theoretical and numerical analysis of the possible errors of this method due to experimental inaccuracies is made. Inaccuracies in oxide thickness, substrate impurity concentration, asymptotic capacitances at strong inversion and accumulation, stray capacitance, absolute capacitance and voltage readings are considered. In addition, errors due to neglecting recombination at interface surface states, bulk states, surface channels and to series resistances are considered. The errors in the total interface density of state calculation can be minimized so that the method is sensitive to densities to 2×109 states/cm2-V in a range of E - Ei = ±14kT in SiSiO2 MOS diodes at 300°K. The main contribution to error in this range comes from assumed inaccuracy in the absolute capacitance reading (±0.002 pF), the stray capacitance error (±0.01 pF) and the asymptotic capacitance errors (±0.002 pF). Near the band edges, the error increases rapidly, to 1013 states/cm2-V at the band edge for inverted surface and to 1011 states/cm2-V at the band edge for accumulated surface. The main source of error at the band edge for surface accumulation comes from the absolute accuracy of capacitance reading. For the inverted surface, inaccuracies due to both the absolute accuracy of capacitance reading and asymptotic capacitance contribute. By using substrate materials of both conductivity types, this method is then sensitive to total (all time constants) interface state density of a few times 109 states/cm2-V over an energy range of 28kT centered at the midgap and to density of 1011 states/cm2-V at the band edge. © 1969.