Deep-level transient spectroscopy: Increased accuracy of interpretation of silicon/silicon dioxide interface state data by the assistance of computer simulations

Abstract

Computer simulations of small filling pulse deep level transient spectroscopy (DLTS) measurements of Si/SiO2 interface states in metal-oxide semiconductor (MOS) capacitors, demonstrate that the time dependence of the surface potential during emission and capture of charge carriers must be considered for a correct interpretation of DLTS data. It is demonstrated that not only the amplitude but also the shape of DLTS spectra are influenced by the interface state density Nit. Accurate values of Nit and capture cross sections are obtained for exponential as well as nonexponential emission of charge carriers by fitting simulated to experimental data. This solves the problem of nonexponential transients due to a time dependent surface potential for high interface state densities. Measurements on irradiated MOS samples verify that numerical simulations can be used for accurate determination of interface state parameters. An observed discrepancy between the amplitudes of the measured and simulated DLTS signals is explained by surface potential fluctuations and a nonuniform lateral distribution of interface states.