Study on Retention Model and Anneal Processing for Charge Storage Layer of SONOS Memory
|School||Huazhong University of Science and Technology|
|Course||Materials Physics and Chemistry|
|Keywords||SONOS memory annealing retention trap distribution storage layer|
With the increase of storage requirement, the market of Nonvolatile memory expandsvery quickly, especially the flash memory. So the development of flash memory hasattracted more attention. SONOS memory can avoid the disadvantages of floating gatememory which are low coupling rate, the disturb of floating gate, high operating voltageand high leakage current, have a lot of advantages such as simple process, fast operatingspeed, long retention time, high storage density. And it becomes the potential memory inthe future. So to improve the characteristics of SONOS memory is the researching point. Inthis paper, SONOS memory is studied, some high k materials with post-depositionannealing in different atmospheres are proposed to replace Si3N4as the trapping layer ofSONOS. A retention model is presented to analyze the effect of trap distribution onretention.In this paper, Charge-trapping memory capacitor with LaTiON or HfLaON as chargestorage layer is fabricated by reactive sputtering method, and influences of post-depositionannealing (PDA) in NH3or N2ambient on its memory characteristics are investigated. Theresult indicates that Ti-NH3has better retention characteristic and Program/Erase speedamong LaTiON samples, but has worse endurance characteristic; Hf-NH3has the beststorage characteristic among HfLaON samples. With the comparison of HfLaON samplesand LaTiON samples, Hf-NH3has the best storage characteristic. So the HfLaON samplewith PDA in NH3is the potential material in the future.In this paper, the effect of tunneling layer thickness、trap energy level and temperatureon the main charge de-trapping mechanisms (trap-to-band tunneling and thermal excitation)is studied. It is found that trap-to-band tunneling is the main charge de-trapping mechanismin the room temperature. Then a retention model considering the effect of trap distributionon retention characteristic is presented, and the effect of trap space distribution and trapenergy distribution on retention characteristic is analyzed. The results show that the trapspace distribution--box distribution is useful to improve the retention; when tunneling layeris thick, trap energy distribution—tri distribution is helpful to improve the retention; whentunneling layer is thin, trap energy distribution—box distribution is useful to improve theretention.The trap space distribution of LaTiON or HfLaON is analyzed with the retentionmodel. It is indicated that the trap space distribution of LaTiON samples is uniformdistribution; but the trap space distribution of Hf-no and Hf-NH3is box distribution; that ofHf-N2is uniform distribution. It is confirmed that the trap space distribution of HfLaON sample is adjusted through PDA in N2ambient. According to correction factor, it is inferredthat LaTiON sample with PDA in NH3has the deepest trap energy level; HfLaON sampleshave the shallower trap energy level than LaTiON samples.