The Process Optimization And Charge Loss Characteristics Investigation Of HfAlO For Trapping Layer

Flash memories are the dominant devices in current non-volatile semiconductor memorymarkets. With flash memory entering20nm technology node, the conventional poly-siliconfloating gate (FG) flash memory meets its serious problems of the scalability.Discrete ChargeStorage Memory, as a technology improvement has received widly attention, due to itslocalized charge storage and coupling-free structure.Discrete Charge Storageincludesnanocrystals memory (NCM) and charge trapping memory (CTM). CTM storage charges byusing thin film which containing largenumber of natural defects. Meanwhile, High-k materialsare applied to decrease the equivalent oxide thickness (EOT), and improve the performance.HfAlO as a High-K material therefore becomes a potential candidate due to its characteristicsof possessing the advantages of both HfO2and Al2O3. This work focused on the researchabout the Charge Trap Memory including bandgap engineering of high-k material as chargestorage layer and charge loss characteristics investigated by Kelvin Probe ForceMicroscopy(KFM).In the field of bandgap engineering of high-k material as charge storage layer,weproposed CTM cell structures consisting of HfO2and Al2O3compounds as trapping layersandwiched between SiO2tunnel layer and Al2O3blocking layer. The proposed trapping layerexhibits large memory window, low operating voltage, high speed, and improved dataretention compared with single HfO2tapping layer, due to the high dielectric constant ofHfO2and appropriate band offset of HfO2to Al2O3. To further explore the conclusion, theimpact of deposition sequence of HfO2/Al2O3on memory performance is investigated. It isfound that the HfAlO samples stacked in the sequence of1nmHfO2/1nmAl2O3and1nmHfO2/2nmAl2O3have the best performance and reliability because of the extra inserted interfacebetween HfO2and Al2O3.In the field of charge loss characteristics investigation，Kelvin probe force microscopy(KFM) technology was applied to investigate the charge storage and loss characteristics ofHfAlO charge trapping layer with various Al contents. The experiment results demonstratethat with Al contents increased in the HfAlO trapping layer, trap density is significantlyincreased. Improvement of data retention characteristic was also observed. Comparing thevertical charge leakage and lateral charge spreading of the HfAlO trapping layers, the formerplays the dominant role in the charge loss mechanisms. Variable temperature KFMmeasurement shows that the extracted effective electron trap energies increase with theincreasing of Al contents in HfAlO trapping layer, which is in accordance with the charge losscharacteristics.