Deffect profiling in the SiO2/ Al2O3 interface using Variable Tcharge-Tdischarge Amplitude Charge Pumping (VT2ACP)

Abstract

A Variable Tcharge-Tdischarge Amplitude Charge Pumping (VT²ACP) is used to profile defect in the SiO2 and Al2O3 separately in Flash Memory based devices. It is shown that by independently controlling the pulse low timing “discharging time” and high level timing “charging time”, the contribution of interface and bulk Al2O3 traps can be separated. By using the ellipsometry and the measured intersection time tcharge to trap in the high- k (∼60 μs), SiO2 thickness of 0.87 nm and scanning rate of 0.19nm/dec is found. Using a slanted wafer, the result shows that in the case of thin SiO2 (∼1nm) the trap density close to the substrate (short tcharge) is one order of magnitude higher compared to thick SiO2 (∼3nm). For tSiO2 = 1.7nm all traps are in the SiO2 or SiO2/Al2O3 transition layer. Only for the thickest SiO2 layers (2.7 and 3 nm) the trap density becomes low and constant. Additionally WKB-approximation is used to calculate the filling probability of the traps (fT), the modeled scanning rate nearly doubles to ∼0.29 nm/dec and 0.27 nm/dec for amorphous and crystalline, respectively. In summary, the method of trap energy/depth profiling by using VT²ACP allows scanning from ∼0.5nm up to 1.2nm in depth and 0.1 to 0.7eV in energy range above the Ec^Si band depending on sample used. The results show that there exist significant interaction between SiO2 and Al2O3 when processed with PDA 1000°C. For amorphous Al2O3 (PDA 700°C) the impact of the precursor is not reflected in the SiO2 trap density while for crystalline Al2O3 no increase in trap density at 0.3eV above the Ec^Si band is observed.