Tunnel Oxide Nitridation Effect on the Evolution of $V_{t}$ Instabilities (RTS/QED) and Defect Characterization for Sub-40-nm Flash Memory

Abstract

We report the impact of tunnel oxide nitridation (TON) on the evolution of random telegraph signal (RTS) and quick electron detrapping (QED) and investigate their microscopic origin. Applying nitridation at the SiO 2 /Si interface increases both Fermi level (RTS) and general midgap (QED) defects in fresh devices. However, it slows down additional defect generation and demonstrates improvement after severe program/erase cycling. Results from low-frequency 1/f noise indicate that TON aggravates RTS for high energy defects but hardens low energy defects, resulting in improved postcycled RTS. The suggestive defect chemistry is that strong Si-N bonding replaces relatively stable (but distorted) Si-O bonding, rather than passivating high energy dangling bonds. The Si-N bonding also causes more interface bonds to break, reducing strain and improving immunity against Fowler-Nordheim stress.Index Terms-Defect chemistry, Flash memory, low-frequency (LF) 1/f noise, multilevel cell (MLC), nitridation, oxynitride, quick electron detrapping (QED), random telegraph signal (RTS), tunnel oxide.

The Impact of Tunnel Oxide Nitridation to Reliability Performance of Charge Storage Non-Volatile Memory Devices

“…54 Secondary Ion Mass Spectroscopy (SIMS) results show the reduction in hydrogen contained in re-oxidized tunnel oxide indicating that dangling bonds due to broken Si H bonds were supplanted by Si O bonding through POA. 54 In light of recent publications by Kim et al 46 47 76 the role of TON onto defect generation and evolution of V t instabilities were extensively studied and reported. TON hardening against FN stress damages is attributed to the replacement of distorted yet stable Si O bonds with strong Si N bonds instead of passivation of dangling bonds.…”

Comprehensive Understanding on the Role of Tunnel Oxide Top Nitridation for the Reliability of Nanoscale Flash Memory

“…While increased parasitic capacitance from an adjacent cell requires thinner tunnel oxide (TO), reduced cell capacitance requires thicker TO for adequate retention. Traditional bottom nitridation of TO, incorporating nitrogen in the oxide near the cell's channel, has been implemented to harden the TO and reduce the damage from the high-field Fowler-Nordheim (FN) stress or channel hot carrier [2], [3]. Top nitridation (TN), such as decoupled plasma nitridation (DPN) and remote plasma nitridation, has been used for CMOS logic devices in which the main purpose was to reduce the gate leakage without excessive mobility degradation [4].…”

Reliability of NAND Flash Memories: Planar Cells and Emerging Issues in 3D Devices

“…Different values were found in NOR arrays, owing once more to differences in cell design and cycling conditions. Such dependences prompted several works and studies on the optimization of the cell process/architecture in order to reduce the extent of the RTN [124,[126][127][128][129][130][131][132][133][134]. In the NAND array, moreover, the RTN amplitude was shown to depend on the cell position and state along the string [135,136] (because of the different transconductances, depending on the source and drain series resistances) and on the state of cells on adjacent BLs [137] (because of the modification in the electron density profile induced by electrostatic interference).…”