Impact of SiN Composition Variation on SANOS Memory Performance and Reliability Under nand (FN/FN) Operation

Abstract

Abstract-Despite significant advances in structure and material optimization, poor erase (E) speeds and high retention charge loss remain the challenging issues for charge trap Flash (CTF) memories. In this paper, the dependence of SANOS memory performance and reliability on the composition of silicon nitride (SiN) layer is extensively studied. The effect of varying the Si:N ratio on program (P)/E and retention characteristics is investigated. SiN composition is shown to significantly alter the electron and hole trap properties. Varying the SiN composition from N-rich (N + ) to Si-rich (Si + ) lowers electron trap depth but increases hole trap depth, causing lower P state saturation but significant overerase, resulting in an enhanced memory window. During retention, P state charge loss depends on thermal emission followed by the tunneling out of electrons mostly through tunnel dielectric, which becomes worse for Si + SiN. Erase state charge loss mainly depends on hole redistribution under the influence of internal electric fields, which improves with Si + SiN. This paper identifies several important performances versus reliability tradeoffs to be considered during the optimization of SiN layer composition. It also explores the option for CTF optimization through the engineering of SiN stoichiometry for multilevel cell NAND Flash applications.Index Terms-Charge trap Flash (CTF), program/erase (P/E) window, retention, SANOS, silicon nitride (SiN), SONOS.

Study of P/E Cycling Endurance Induced Degradation in SANOS Memories Under NAND (FN/FN) Operation

“…• C [28], [30]. Table I summarizes the device details with the flow ratios and measured refractive index (RI) of different gate stacks.…”

Charge Retention Improvement of Nonvolatile Radiation Sensor Using Metal–Oxide–Nitride–Oxide–Silicon with Si-Rich Nitride and Oxy-Nitride as Stack Charge-Trapping Layer

“…This result also agreed with previous studies for a MONOS device with a Si rich nitride charge-trapping layer. (11,12) Furthermore, a much deeper negative-charge E TA was observed for O-MONOS with an oxy-nitride trapping layer than for STD-MONOS. This result also agreed with the previous study of a MONOS device with an oxy-nitride charge-trapping layer.…”

“…For preirradiated S-MONOS, a larger negative-charge-loss with retention time was observed due to the relatively shallow negative-charge trap energy level (E TA ) originating from Si-H or Si dangling bonds, which causes significant thermal excitation of trapped negative charges to the nitride conduction band. (11,12) The result shows that high silicon composition ratio in the trapping nitride layer led to worse negative charge retention reliability characteristic of pre-irradiated S-MONOS. The figure shows that the trend in charge retention loss with time for S-MONOS after 10 Mrad gamma irradiation is exactly opposite to that before gamma irradiation.…”

“…This result also agreed with the previous study for the Si-rich nitride chargetrapping layer in a MONOS device. (11,12) Relatively shallow negative-charge trap energy levels (E TA ) originating from Si-H or Si dangling bonds were observed for S-MONOS (compared to STD-MONOS). This result also agreed with previous studies for a MONOS device with a Si rich nitride charge-trapping layer.…”

“…This result also agreed with the previous study of a MONOS device with an oxy-nitride charge-trapping layer. (11,12) …”