TOTAL-IONIZING-DOSE EFFECTS ON CHARGE-TRAPPING NAND MEMORY DEVICES

Abstract

Total ionizing dose (TID) effects are important to consider for nonvolatile memories used in high-radiation environments. Nowadays NAND Flash memory devices are based primarily on 3D NAND architecture due to their advantages for high density storage. Vertical NAND stacks based on silicon-oxide-nitride-oxide-silicon (SONOS) memory cells are increasingly used for 3D NAND memories, and generally are more radiation-tolerant than floating-gate Flash memories. In this paper, TID effects are evaluated in vertical-charge-trapping NAND devices with silicon oxynitride (SiON) and SiO2 tunneling layers. Processing splits include SiON tunneling layers with and without H2/D2 high-pressure annealing. Programmed devices were irradiated to 500 krad(SiO2) with 10-keV X-rays and annealed for 30 min. The effects of geometry and cycling are also evaluated for devices with SiON tunneling layers. Programmed and erased devices were irradiated and retention and endurance performance were evaluated both before and after irradiation. Scaling devices to smaller dimensions enhances program/erase efficiency and radiation tolerance. Excellent retention and endurance are demonstrated for these devices before and after irradiation. Throughout the full irradiation, annealing and reliability test sequence, threshold voltages remain large enough to enable successful NV memory application.