Study On Reliability Improvement Of 0.35 Micron SONOS Nonvolatile Memories Device

As the market demand is increasing for a higher level of integration in flash memory devices, traditional flash memories are much more exposed to problems arising from reliability, working speed, power consumption and size limitations. It is widely convinced that the poly-silicon floating - gate flash devices, when being reduced to less than 45nm in size, will be definitely replaced by new generation memory technologies.Therefore, the non-volatile memory (NVM) devices based on new storage mechanisms have caught broad attention from the industry researchers. Such devices include SONOS memory, nano memory, phase-change memory (PCM), ferroelectric random access memory (Fe-RAM), and magnetic random access memory (MRAM). Among those, SONOS memory, known as its charge-trapping structure, replaces traditional floating - gate memory structure with a stacking structure of―silicon (substrate) - tunnel oxide– oxy-nitride-blocking oxide– poly-silicon (Silicon - Oxide - Nitride - Oxide– Silicon, or SONOS)‖. Due to its highest compatibility with traditional flash memories in terms of structure and process technology, SONOS NVM is most likely to effectively replace traditional flash memories as fast as possible.By identifying the reliability deficiencies existing in a 0.35?m SONOS device designed by Company X, this paper first analyzes the charge transmission mechanism of SONOS NVM. Then, a detailed research is developed on how to improve the structure of Oxide - Nitride - Oxide (ONO) stacks and how to achieve the optimization of materials forming the ONO. During the experiments illustrated in this paper, the in-situ method is first introduced in forming the ONO structure to fabricate SONOS; a measurement and analysis of C-V and I-V characteristics are next conducted on SONOS capacitors to demonstrate the ability of quantum dots to capture charges; then the same structure is used in the fabrication of memory devices; read/write characteristics measurement of the fabricated devices is conducted finally and the reliability parameters are further analyzed to evaluate their influences on data retention and endurance performance of SONOS structure.This paper discusses a series of ways to improve the reliability. Those ways include improving the influence of GOX pre-cleaning on the thickness of HTO to reach a better data retention, utilizing oxy-nitride grading to improve data retention and endurance, introducing ND3 into ONO stack to improve data retention and endurance, and introducing N2O into tunnel oxide layer to improve endurance. The research demonstrates that the reliability of SONOS devices can be greatly enhanced by improving data retention and endurance, which are the two key parameters for reliability.