Pillar Type Silicon-Oxide-Nitride-Oxide-Silicon Flash Memory Cells with Modulated Tunneling Oxide

Abstract

In this paper, we fabricated 3D pillar type silicon-oxide-nitride-oxide-silicon (SONOS) devices for high density flash applications. To solve the limitation between erase speed and data retention of the conventional SONOS devices, bandgap-engineered (BE) tunneling oxide of oxide-nitride-oxide configuration is integrated with the 3D structure. In addition, the tunneling oxide is modulated by another method of <TEX>$N_2$</TEX> ion implantation (<TEX>$N_2$</TEX> I/I). The measured data shows that the BE-SONOS device has better electrical characteristics, such as a lower threshold voltage (<TEX>$V_{\tau}$</TEX>) of 0.13 V, and a higher <TEX>$g_{m.max}$</TEX> of 18.6 <TEX>${\mu}A/V$</TEX> and mobility of 27.02 <TEX>$cm^2/Vs$</TEX> than the conventional and <TEX>$N_2$</TEX> I/I SONOS devices. Memory characteristics show that the modulated tunneling oxide devices have fast erase speed. Among the devices, the BE-SONOS device has faster program/erase (P/E) speed, and more stable endurance characteristics, than conventional and <TEX>$N_2$</TEX> I/I devices. From the flicker noise analysis, however, the BE-SONOS device seems to have more interface traps between the tunneling oxide and silicon substrate, which should be considered in designing the process conditions. Finally, 3D structures, such as the pillar type BE-SONOS device, are more suitable for next generation memory devices than other modulated tunneling oxide devices.