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Tunnel Oxynitride Film Formation for Highly Reliable Flash Memory
Tomiyuki ARAKAWA Ryoichi MATSUMOTO Takahisa HAYASHI
IEICE TRANSACTIONS on Electronics
Publication Date: 1996/06/25
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on ULSI Memory Technology)
Category: Nonvolatile memories
flash memory, oxynitride tunnel film, endurance, disturbance, retention,
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A tunnel film(9 nm thick) formed by a rapid thermal oxidation in dry oxygen-rapid thermal nitridation in NH3-rapid thermal oxynitridation in N2O (ONN) sequence is applied to a stacked-gate flash memory cell, in which writing and erasing are carried out by Fowler-Nordheim tunneling at a drain and at a channel, respectively. The writing, erasing, endurance, disturbance and retention characteristics of the memory cells with ONN tunnel films are, for the first time, compared to those of the memory cells with conventional tunnel films such as dry oxide, N2O-oxynitride and reoxidized nitrided oxide tunnel films. No significant difference of the writing and erasing characteristics was observed among the memory cells with the various tunnel films. However, the amount of Vth window narrowing in the endurance characteristics of the memory cells with ONN (-12.9%) and reoxidized nitrided oxide(-11.4%) tunnel films were much smaller than those of the memory cells with RTO(-34.0%) and NO (-38.2%) after 106 write/erase cycles. Furthermore, the decrease in Vth in the drain disturbance characteristics of the memory cells with ONN tunnel films (21.2%) after weak electron-ejecting stress of 105 cycles was smaller than those of the memory cells with the other films(51.4-64.4%). The retention characteristics of the memory cells with ONN tunnel films under the thermal stress of 200, 5.9105 sec were superior(ΔVth=-2.1%) to those of the memory cells with the other films(ΔVth=-5.4 - -8.2%). The reasons of these findings are because ONN films exhibit smaller number of charge traps and interface states induced by write/erase cycle stress, and suppress leakage curent stimulated by the weak electron-ejecting bias and the thermal stress, compared to the dry oxide, the N2O-oxynitride and the reoxidized nitrided oxide. ONN films are found to be suitable for use as tunnel films of fiash memory cells.