Reliability Comparison of Al2O3 and HfSiON for use as Interpoly Dielectric in Flash Arrays

For the scaling of embedded floating gate (FG) memories towards the 45nm CMOS generation and beyond, a reduction of the program and erase voltages is required. A solution is the use of high-k inter-poly dielectrics (IPD) to increase the coupling of the control gate (CG) to the FG. Compared with standard IPD materials like oxide-nitride-oxide (ONO), materials with higher k-values give a better coupling, but have generally lower tunnel barriers, which can cause data retention issues. Examples of CMOS compatible high-k materials are Hf-based compounds like HfSiON or HfO₂, and Al₂O₃. Although the k-value of Al₂O₃ is lower than for the Hf-based materials, it has higher tunnel barriers for electrons and holes, which is important for high temperature data retention. In this paper, the authors present for the first time flash arrays with Al₂O₃ IPD. The fact that the data were collected on arrays with sizes up to 26kbit greatly improves the relevance in comparison with single cell studies. The cells with Al₂O₃ were benchmarked against cells with HfSiON IPD. A lifetime of 10 years at 125degC was derived for 15nm Al₂ O₃ IPD, which should be compared with a lifetime of 10 years at 80degC that was found for 25nm HfSiON in a previous study (van Duuren, et al, 2006)