Based On The Storage Effect Of Ru-ruo_x Nanocrystalline And High-k Dielectric Mos Structure And Mechanism

With development of semiconductor technology and downscaling of the memory device, conventional poly-silicon floating gate flash memories are facing severe challenges. Embedded nonvolatile flash memory devices based on discrete charge storages have recently drawn great attention as a promising replacement of the conventional poly-silicon floating gate structure due to improved retention characteristics in the case of a thinner tunneling layer, and faster program/erase (P/E) speed under lower operating voltages. Based on discrete dielectric traps, metal nanocrystals and compound of the two structures as charge storage media, in combination with atomic-layer-deposited high permittivity (k) dielectrics and e-beam evaporation high work function metal electrode, this thesis presents memory effects of the corresponding metal-oxide-silicon (MOS) structures, and the involved physical mechanisms are also discussed. The details include the following sections:(1) Growth of Ru-RuOx composite nanodots (RONs) on atomic-layer-deposited Al2O3 film has been investigated using magnetic sputtering of Ru target followed by post-deposition annealing (PDA). The results reveal that the RONs with a small size of 5～6 nm, high-density of～2×1012 cm-2 and good uniformity have been achieved for the PDA at 900℃for 30 s. Subsequently, the electrical characteristics of MOS capacitor with RONs embedded into ALD Al2O3 dielectrics have been measured, indicating a C-V hysteresis window as large as 11.2 V at -11～+11 V sweeping gate voltage. In order to further investigate the influence of different configurations of tunneling-layer (T)/blocking-layer (B) on memory effect, various MOS capacitors with RONs-embedded into ALD Al2O3 insulator have been fabricated using a high work function Pd electrode. The resulting C-V hysteresis window and effective injected charge density exhibit significant dependence on the configuration of T/B in the case of low gate voltages, and approach equal regarding high gate voltages. This is due to different tunneling barriers associated with direct tunneling mechanism dominated under low gate voltage and F-N tunneling mechanism under high gate voltage. With regard to the configuration of T/B=6-nm/22-nm, a memory window as large as 5.1V is achieved for P/E at a low voltage of +/-7 V for 1 ms, and superior charge retention of more than 80% is achieved after ten years.(2) Using hybrid high-k dielectrics with different ratio of Al2O3/HfO2 (A/H) as a charge trapping layer, various MOS memory capacitors have been fabricated. The electrical characteristics of MOS capacitors were investigated and it reveals that with increasing HfO2, the capability of charge trapping improves and the retention time of charge storage decreases. When the charge trapping layer is pure HfO2, the C-V hysteresis window of MOS capacitor can reach 3.6 V under+/-14 V sweeping voltage. Further, after being programmed at+17 V for 10 ms, its flat band voltage (Vfb) drifts towards positive for +2 V. However, only about 55% charges are retained in HfO2 half hour later, and the leakage current of MOS capacitor becomes as large as 1.4×10-5 A/cm2. This is attributed to the low HfO2 crystalline temperature, which leads to a large leakage current along the grain boundary.(3) Using compound of the Ru-RuOx NCs/High-k dielectric as a charge trapping layer, ALD Al2O3 as tunneling and blocking layer, various MOS capacitors with Pd electrode have been fabricated. Compared to single Ru-RuOx NCs charge trapping layer, the compound one can increase significantly the C-V hysteresis window. When the high-k trapping layer is pure HfO2, the C-V hysteresis can increase by 10.3 V for +/-9 V sweeping voltage. This is attributed to an enhancement of the electric field dropping on the tunneling layer, and it helps to increase the charge injection rate. Therefore, the MOS capacitor with Ru-RuOx/HfO2 charge trapping layer exhibits a perfect memory window as large as 3.4 V for 100μs P/E at a low voltage of +/-9 V, which is associated with fast charge injection rates, i.e.,～2.8×1011 cm-2s-1 for electrons and～3.0×1011 cm-2s-1 for holes. Also it shows superior charge retention characteristic after ten years.