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

Abstract

This paper is written to review the development of critical research on the overall impact of tunnel oxide nitridation (TON) with the aim to mitigate reliability issues due to incessant technology scaling of charge storage NVM devices. For more than 30 years, charge storage non-volatile memory (NVM) has been critical in the evolution of intelligent electronic devices and continuous development of integrated technologies. Technology scaling is the primary strategy implemented throughout the semiconductor industry to increase NVM density and drive down average cost per bit. In this paper, critical reliability challenges and key innovative technical mitigation methods are reviewed. TON is one of the major candidates to replace conventional oxide layer for its superior quality and reliability performance. Major advantages and caveats of key TON process techniques are discussed. The impact of TON on quality and reliability performance of charge storage NVM devices is carefully reviewed with emphasis on major advantages and drawbacks of top and bottom nitridation. Physical mechanisms attributed to charge retention and V(t) instability phenomenon are also reviewed in this paper.

Investigation on the origin of the anomalous tail bits on nitrided charge trap flash memory

“…This indicates the defects density induced by the extensive repeated cycles charge injections in P/E cycling intensifies the underlying CL mechanism of nitrided NBCTF memory. With the implementation of FN tunneling as charge injection mechanism, extensive P/E cycling will typically result in defects such as bulk oxide traps and charge trapping (CT) interface states [1][2][3][4]. As shown in Fig.…”

“…The silicon nitride layer acts as the designated charge trap layer which is sandwiched between the top silicon oxide layer and tunnel silicon oxide layer. The intrinsic defects in silicon nitride layer which surrounded by oxide layers inherently trap injected charges during P/E operations [1][2][3][4]. The top and tunnel silicon oxide layers provide sufficient protection to prevent charge leakage due to direct tunneling of charges from silicon nitride layer.…”

“…Nevertheless, there are three critical limitations that prevent further technology scaling on FG flash memory, i.e. (1) severe stress induced leakage current (SILC) triggered if the tunnel oxide layer is scaled to less than 8 nm; (2) gate coupling ratio of minimum 0.6 has to be met in order for control gate of FG flash memory to properly exert control to FG and the channel; (3) severe cellto-cell interference [1][2][3][4][5][6][7][8]. As compared to FG flash memory, NBCTF memory enables better downscaling of the tunnel oxide layer while still preserving overall good data retention performance.…”

“…As compared to FG flash memory, NBCTF memory enables better downscaling of the tunnel oxide layer while still preserving overall good data retention performance. However, the downscaling of tunnel oxide layer of NBCTF memory has to be complemented with innovative approaches to continue the technology scaling trend for NBCTF memory [3,4]. Tunnel oxide nitridation (TON) is one of the approaches applied together with the downscaling of tunnel oxide layer in order to enhance the immunity of NBCTF memory to Fowler-Nordheim (FN) stress induced damages in tunnel oxide layer.…”

“…Tunnel oxide nitridation (TON) is one of the approaches applied together with the downscaling of tunnel oxide layer in order to enhance the immunity of NBCTF memory to Fowler-Nordheim (FN) stress induced damages in tunnel oxide layer. By implementing various wet or dry nitridation processes, TON is done by incorporating nitrogen content into the tunnel oxide layer to achieve larger memory window and better hardening towards the damages due to extensive program/erase P/E) cycling stress through FN injection [1][2][3][4][5][6][7][8][9][10]. Nevertheless, TON was also found to result in several critical reliability issues such as Fermi-level defects and mid-gap defects.…”