Investigation of theoretical limitations of recombination DCIV methodology for characterization of MOS transistors

This dissertation investigates the accuracy of using the recombination direct-current current voltage (R-DCIV) method to measure the interface traps and spatial variations or profiles of impurities and oxides in silicon MOS transistors. The Boltzmann electron-hole distribution and ionized impurity approximations (Boltzmann ionization or BI) are much faster than the Fermi-Deionizated (FD) model. The accuracy of using the BI approximation to extract the device and material parameters of an MOS transistor is investigated by comparing with the time-consuming and complicated FD model. The accuracies or confident levels on the extractable device and material parameters are analyzed, such as dopant impurity concentration PAA, oxide thickness XOX , interface trap concentration NIT, injected minority carrier concentration at SiO2/Si interface represented by the p/n junction VPN, energy level of interface traps distribution in silicon gap ETI and temperature T. From R-DCIV lineshape analyses, it is shown that the BI approximation gives a small (1%∼5%) deviation when matching 90% of the experimental DCIV curve to theory. These results indicate that the simple and time-saving BI approximations are sufficiently accurate to extract from experimental data the spatial profiles of the dopant impurity concentration, and interface trap concentration at the SiO2/Si interface, and oxide thickness in modern MOS transistors.; Effects of energy distribution of the interface traps on the R-DCIV lineshape are also investigated. Comparison are made among three density of state (DOS) distributions of interface traps (1) a U-shaped DOS, (2) a constant DOS, and (3) a discrete interface trap energy level at mid-gap. These comparison shows that the experimental broadened R-DCIV lineshapes may also be accounted partially for the spatial variation of surface dopant impurity concentration but also by the energy distribution of interface traps in silicon gap. Slater's perturbation theory is employed to suggest that a U-shaped DOS is the most probable distribution in silicon gap. Thus, the extractions of parameter spatial profiles, from experimental, should use a U-shaped density of interface traps, instead of the commonly assumed trap level at mid-gap ETI=0 in the silicon energy gap.; For both the continuous energy distribution of interface traps and a discrete interface trap energy level at midgap, the peak R-DCIV current has large temperature dependence. However, the thermal activation energy, the lineshape, reciprocal slope, and peak gate voltage all have negligible temperature dependence. The analyses of impurity deionization effect show that deionization has a negligible effect on the R-DCIV lineshape when using Fermi ionization approximation (FI) to match experimental data from peak current down to 10% of the peak. The errors of FI approximation are nearly identical to the confident level of BI for all device and material parameters in practical range, for both metal gate and silicon gate MOS transistors.