Suppression of Oxide Encroachment into Floating Gate by Shallow Trench Isolation Recess in an Electrically Erasable Programmable Read Only Memory Cell

Abstract

In this paper, we investigate the effects of the oxide recess in shallow trench isolation ͑STI͒ on the characteristics of electrically erasable programmable read only memory ͑EEPROM͒ cell with in situ-doped floating gate. It is found that the distribution of the program threshold voltage is improved with increasing of the oxide recess in STI. Transmission electron microscopy analysis shows that the oxide recess in STI results in the decrease of oxide thickness at the edge of STI and in the center of tunnel oxide. Also, it is observed that erase cell current is increased about 11% with oxide recess of 200 Å and 21% with oxide recess of 400 Å, respectively. Endurance measurements in the EERPROM cell reveal that both electron and charge generation increase with increasing recess depth when the cycling time exceeds about 1 ϫ 10 3 .