Abstract
In recent years, flash memory device can be continuously scaled down by continuous advance in process technology. However, the scale down of planar flash memory device can not be continued due to its limitation of shrinkage. How to increase the density of memory devices and enhance operating characteristics are important issues. Some approaches have been reported to solve these issues, such as high-k material, junctionless (JL) channel, poly-Si channel, nanowire (NW) structure, gate all around (GAA) structure and 3D stack devices. In this thesis, operation characteristics of flash memory GAA devices are improved by enhance electric field at channel cornors. Operation characteristics of GAA device with different charge trapping layers and blocking oxides layers are also studied. In the first part, tunneling oxides of devices with NW and GAA structure are formed by low-temperature inductively coupled plasma chemical vapor deposition (ICPCVD) and high-temperature rapid thermal oxidation (RTO) and Si3N4/HfO2 trapping layers are applied. In this work, program speed of gate all around device is faster than that of NW one due to larger enhancement of electric field. Reliabilities of GAA decice are worse than that of NW one due to poor step coverage of tunneling oxide layers are formed by ICPCVD. In the second part, Si3N4/HfO2 and Si3N4/ZrO2 stacked trapping layers are deposited by low-pressure chemical vapor deposition (LPCVD) and atomic layer deposition (ALD), and tunneling oxides are formed by RTO. Device with Si3N4/ZrO2 stacked trapping layers shows faster erasing speed are compared to that with Si3N4/HfO2 ones. Additional Al2O3 trapping layer are added between Si3N4 and HfO2 or ZrO2 layer. Results show that both retention and endurance are improved by the additional Al2O3 layer. In the last part, effects of stacked blocking oxide layers on operation characteristics of GAA flash memory devices are investigated. Results show that programing and erasing speed of devices with or without stacked blocking layers are similar. Retention characteristics at high-temperature are improved by stacked blocking oxide layers.