|M.Sc Thesis||Department of Materials Science and Engineering|
|Supervisor:||Prof. Eizenberg Moshe|
The application of Cu metallization in modern microelectronic devices requires an effective barrier, in order to prevent the detrimental effect of Cu diffusion into SiO2 and Si. Electrical characterization methods are highly sensitive to Cu and are therefore employed in many studies of diffusion barriers for Cu metallization. One of the most commonly used methods for studying Cu diffusion into Si devices, is the measurement of Capacitance-Voltage (C-V) characteristics of Metal-Oxide-Semiconductor (MOS) capacitors, before and after applying Bias Thermal Stress (BTS) cycles.
This work is focused on understanding the influence of bias-enhanced Cu diffusion on the electrical properties of MOS capacitors. This influence is tested using various electrical methods such as steady state, quasi-static and deep depletion capacitance-voltage (C-V) measurements, capacitance transients (C-t), current-voltage (I-V) and TVS (Triangular Voltage Sweep) measurements.
Research results show that the penetration of Cu causes significant changes in the capacitor's electrical properties. The presence of Cu ions in the oxide is detected by negative flatband voltage shifts and by the appearance of a characteristic peak in TVS measurements. Other electrical methods show that Cu increases the state density at the SiO2/Si interface, decreases the minority lifetime in the Si and enhances oxide degradation.
In this study, a previously unreported form of Cu related degradation in SiO2 is demonstrated and explained. This form of degradation increases the oxide conductivity to a level, which is enough to enable the leakage of minority carriers generated at the inversion layer, while the C-V characteristics can still be accurately measured. The study re-assesses the validity of the C-V BTS method for characterization of Cu diffusion in MOS capacitors, showing that a full characterization of the capacitor's properties is needed in order to correctly extract quantitative results.