| Microelectronics is in the positon of the most important status in the modern technology revolution,the wide use of large scale integrated circuit is not only an important achievement of the development of the microelectronics,but also a significant symbol of it.With the decreasing of the size of the microelectronics devices,the basic operating mode of the traditional microelectronics devices is becoming more and more inapplicable while charge quantization effects and energy quantization effects play a significant role in such devices,and the traditional microelectronics technology is faced with serious challenges.In order to meet these challenges,scientists and entrepreneurs concentrating on the research and development of the new generation of nanoelectronics devices,and nanoelectronics devices is the important foundation of the target of the large scale integrated circuit to become faster,smaller and lower power consumption.Moreover,it represents the development direction of the material of the whole information technology.With the development of the function integrated circuits and the require of digital information technology,the proportion of the semiconductor memory in large scale integrated circuit becomes larger and larger.Thus,it is of great importance to fabricate a high performance semiconductor memory for the development of nanoelectronics and information technology.This thesis devotes to the research and fabrication of nonvolatile memory based on silicon nanocrystals.With the guide of the theoretical mode of Quantum confinement effect,coulomb blockage effect and single electron resonant tunneling etc,we fabricate the SiO2/nc-Si/SiO2 asymmetric double barrier structure in PECVD system by using Layer-by-Layer technology combined with plasma oxidation method.The electrical properties of SiO2/nc-Si/SiO2 asymmetric double barrier structure is studied by I-V measurements,and clear multi current peaks for electrons and holes in the I-V curves were prove to be induced by electrons and holes resonant tunneling into the nc-Si quantum dots from the substrate and calculations indicate that these current peaks should be associated to Coulomb blockade effect and quantum confinement effect of the nc-Si quantum dots.In order to get further study of the charge storage mechanism of silicon quantum dots,the change of surface potential caused by the charge injection of the electrons and holes in to the silicon quantum dots is observed by using Kelvin Probe Force Microscopy(KPFM).Based on the experiments above,SiNx/nc-Si/SiO2 floating gate MOS structure was fabricated to investigate the charge storage mechanism of MOS structures containing silicon quantum dots.The C-V measurement of the SiNx/nc-Si/SiO2 floating gate MOS structure confirmed that the flat band shift of the C-V curves is induce by the charge storage mechanism of silicon quantum dots.The improvement of the C-V characteristics by using thermal annealing is also investigated for the successive fabrication of the floating memory based on silicon quantum dots.In order to applicate the charge storage mechanism of Si quantum dots successfully into the MOSFET floating gate memory,we investigated the key technology to fabricate the ultrathin tunneling oxide,silicon quantum dots and control layer.After that,a set of photolithography mask template and process flows are carried out based on the 5inch standard CMOS process flows to fabricate the nc-Si MOSFET floating gate memory.The structure is proved to be sufficient in electron write and erase and can keep the carriers effectively in the silicon quantum dots based on the results of the I-V test.Furthermore,the single cell of the nc-Si quantum dot floating gate memory is arranged into 4×4 NOR flash array to checkout the function of a single cell in the memory array,and the experiment results suggest that the single cell can write,erase and read effectively in the NOR flash memory array.We also investigated the relationship between the device characteristics and the parameters of the ultrathin tunneling oxide,silicon quantum dots and control layer,The conclusions are as follows:The speed of the charge storage is faster when the tunnel oxide is 2.5nm,but the charge is more probable to tunnel back into the channel,therefore suffered a worse retention characteristics and a smaller charge window.On the other hand,a 4.5nm tunnel oxide induced a longer retention time but the speed of the charge injection is much slow;A 30nm SiNx control layer can not only get a large memory window and fast operating speed,but also can effectively prevent the charge leakage to the gate electrode acting as the charge barrier layer;When the size of the nc-Si quantum dots is 15nm,the nc-Si quantum dot floating gate memory can get a small monodispersity of the initial Vth as well as a large memory window and fast operating speed.In order to meet the requirements of the design of the integrated circuit,the gate length of the nc-Si quantum dot floating gate memory should be reduced considerable.Therefore,the device characteristics with the gate length of 1?m and 3?m are carried out to compare with each other and the experiment results indicate that the charge storage characteristics hardly changed when the gate length reduced.In order to further improve the device characteristics,a nitridation nc-Si quantum dot floating gate memory is fabricated and I-V measurements are carried out to investigate the improvement of the device performance after the nitridation treatment to the nc-Si quantum dots.The silicon nitrided cover layer formed on the surface of Si nanocrystals acted as a passivation layer,therefore,it is expected that the dangling bonds and the density of interfacial states of nc-Si/SiNx could be reduced.The reduction of the interface states apparently enhanced the control effect of gate voltage which induced a larger memory window as well as a faster program speed.On the other hand,the silicon nitrided cover layer also acted as a potential barrier for the carriers tunneling back to the channel which can reduce the tunneling probability of the carriers.Furthermore,the nitrided silicon cover layer also made the Si nanocrystals well separated and the leakage current among the nc-Si dots could be reduced,therefore a longer retention time is also expected.Based on the above research to improve the device performance of the nc-Si quantum dots:floating gate memory fabricated in the 5inch standard CMOS process flows.We fabricate a nc-Si quantum dots floating gate memory with the gate length of 0.176?m in the 0.13?m,8inch standard CMOS process flows of Shang Hai SMIC.By comparing the electrical characteristics of the nc-Si quantum dots floating gate memory with the other groups,we demonstrate that the device performance of the nc-Si quantum dots floating gate memory with nitridation treatment reaches the wold level.The subthreshold swing of the device is less than 0.15V/decade,On/Off ratio is lager than 106,the operating voltage pulse is ±7V/1ms,the charge storage window is lager than 1.5V and the retention time is more than 10 years. |
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