Structure Parameter Optimization And High-k Storage Layer Research Of MONOS Memory

The International Technology Roadmap for Semiconductors of2011proposed that thereexist a lot of challenges in improving the reliability of the charge trapping memory when itssize is scaling down. This paper concentrates on this type of memory. A comprehensiveanalysis of how the charge trapping memory (SONOS(Poly Silicon-Oxide-Nitride-Oxide-Si)/MONOS(Metal-Oxide-Nitride-Oxide-Si)) works and how charges transport in the memoryis done. Both the device simulation tool and the experimental method are used in this study.First, the effect of the thickness of each layer is investigated with Silvaco TCADsoftware simulation, thus the stack thickness of memory cell was optimized and determinedwith a reasonable trade-off among memory window, operating speed, retention andendurance characteristics. Then, memory characteristics of SONOS memory with GdO andLaHfO high-k materials as the storage layer are simulated. It is proved that the high-kmaterial as the storage layer is of significance for achieving practical SONOS memory withlow operating voltage、high speed and excellent retention characteristic.Next, on the basis of experiments, MONOS capacitor memory with oxygen-rich、oxygen-deficient gadolinium oxide (GdO) or GdON as charge storage layer is prepared byreactive sputtering. The XPS analysis method is used to determine the composition of thestored layer material and examine interface characteristics of the storage layer and tunnelinglayer. The results show that the memory window, operating speed, retention characteristicand endurance characteristic of the nitrogen incorporation sample (GdON) are the mostexcellent among three sample, due to its high trap density、deep trap energy level、largedielectric constant and good interface characteristic. Finally, the effects of thepost-deposition annealing of storage layer at N2or NH3atmosphere on the characteristics ofthe memory are studied. Experimental results show that annealing can help to obtain a goodtrade-off among memory window, operating speed, retention and endurance characteristicsfor MONOS memory with suitable atmosphere annealing after depositing GdO(N) memory layer. It is found that the GdON dielectric annealed in NH3has good memory characteristics:P/E at voltage of±14V for1s, the memory window is4.7V; at12V programming voltagefor100μs time it has become saturated; retention at room temperature for10years, the lossof charge is only24%. Therefore, the GdON high-k dielectric with post-deposition annealingin NH3is a promising candidate as the charge storage layer for advanced small-size MONOSnonvolatile memory applications.