Study on application of high-K dielectric materials for discrete charge storage memory

Abstract

Discrete charge storage memories including nanocrystal (NC) memory and SONOS type memory are the most promising candidates to substitute for conventional floating gate memory. Thanks to their isolated charge storage nodes, the discrete charge storage memories are immune to local defect related leakages, therefore providing aggressive scaling capability. In this thesis, the following issues are investigated: formation of NCs, application of high-k dielectric materials for NCs memory and SONOS type memory device, and optimization of the SONOS cell structure. Self-assembled Ge NCs are formed on HfO2 and HfAlO by CVD and by cosputtering method. The Ge NCs are thermally stable in HfAlO matrix. A nonvolatile memory device employing Ge NCs embedded in HfAlO dielectric exhibits excellent memory performance. HfO2 NCs are developed by annealing the HfSiO film at above 900oC. Hf0.5Si 0.5O2 film containing dual phase as a trapping layer is found to provide a faster programming speed at a lower programming voltage than Si3N4 and better retention property than HfO2.Device with IrO2/HfAlO/HfSiO/HfAlO gate stack achieves excellent retention, high erasing speed, and lower operation voltage due to the advantages of high-k HfAlO tunneling and blocking oxide, good trapping capability of HfSiO, and high work function of the IrO2 gate, SONOS type memory device with the dual tunneling layer (Si3N4/SiO2) and a high-k HfO2 charge storage layer demonstrates fast program/erase speed and large memory window due to the high trapping efficiency of high-k materials and the enhanced charge injection from the substrate through the dual tunneling layer, excellent retention due to the physically thick dual tunneling layer and also the improved endurance. Ita??s promising for NAND flash application.