The study on un-doped/boron doped/un-doped triple SEG in vertical NAND flash memory
Keywords:SEG, Vertical Channel Etch, Boron Concentration, GSL Vth, Boron Doped
Selective epitaxial growth (SEG) plays a critical role in vertical NAND flash memory because it serves as a ground select line (GSL) transistor, which is used to control the cell current in the vertical channel. In this study, different channel hole sizes between the adjacent hole and away hole from the common source line (CSL) were detected after vertical channel etch (VCE). This discrepancy severely impacts the boron concentration of SEG applied through ex-situ boron implantation, and results in large GSL Vth variations. Novel in-situ boron-doping of triple-layered un-doped/boron doped/un-doped SEG was developed to solve the high variation of the boron concentration in SEG caused by different channel hole sizes.
A series of experiments was designed and performed to determine the optimal height and concentration of the boron doped SEG. Finally, the optimized boron-doped SEG in the triple-layer SEG was shown to improve the distribution of the GSL Vth without deterioration of the SEG height uniformity.
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