Improvement of Retention Characteristics Using Doped SiN Layer Between WL Spaces in 3D NAND Flash

Abstract

We propose a novel structure of a charge trapping layer, that is doped between Word Line(WL) spaces in 3D NAND flash memory. To estimate the retention characteristics, the $\Delta \text{V}_{\mathrm {th}}$ of each structure by doping type is compared to a reference structure during retention operation. In this study, lateral charge spreading, rather than vertical loss, is mainly studied as an indicator to determine how long stored data can survive on the selected cell. When the SiN layer is doped with p-type, the electrostatic potential decreases and SRH recombination increases in the doping region. As a result, the p-type doping structure has better retention characteristics than others. In addition, for an optimized structure between retention characteristics and cell current, the doping region of the SiN layer is split and analyzed by the thickness of the doping region. Since the p-type doping region is thicker, lateral spreading is effectively blocked although the cell current decreased slightly.

Keywords

• 3D NAND
• doped SiN layer
• electrostatic potential
• lateral charge spreading
• SRH recombination