Effects of active area and gate doping method on program threshold voltage in an EEPROM cell

摘要

In this paper, we investigate dependency of program threshold voltage (V_T) in EEPROM cell on active area and doping method of floating gate. With in situ doped floating gate, it is found that there is a sharp drop of program V_T from 4 to 2.25 V when the channel width is reduced from 0.30 to 0.22 μm, while doping by ion implantation results in slight reduction of program V_T from 3.95 to 3.69 V. It also appears that channel length is another critical factor to affect on reduction of program V_T. In case of in situ doped floating gate, the program V_T is reduced from 3.9 to 2.7 V when the channel length is reduced from 0.20 to 0.18 μm. TEM analysis reveals that thermal oxidation in tunnel oxide region occurs during subsequent high temperature oxidation due to oxidant penetration via interface of silicon surface and sidewall silicon nitride.