Abstract
The tapered channel effect is a major concern in three-dimensional (3-D) NAND technology because the effect causes differences in the electrical characteristics, including the threshold voltage (VT), between the upper and the lower cells. We simulated the tapered channel effect by using Sentaurus technology, computer-aided design (TCAD) tools, and based on the results, we propose a novel method to lessen the non-uniformity of the threshold voltage shift ( ${\Delta }\text{V}_{\mathrm{ T}}$ ) between the cells. The difference in ${\Delta }\text{V}_{\mathrm{ T}}$ between the upper and the lower cells due to the tapered channel can be reduced by employing a tapered blocking oxide layer with a proper taper angle. These results will be helpful in designing reliable 3-D NAND flash memories.
Highlights
TWO-dimensional (2-D) flash memory technologies have faced physical limitations due to the shrinking problem of NAND flash memories [1], [2]
When implementing multi-level technology and high-rise stacking technology to enhance efficiency, several factors affect the variability of 3-D NAND flash memories, and these factors can be classified into three categories [5]: the effect of grain boundary traps [6,7,8,9], fluctuations in the control of the critical dimension [10], and the effect of the tapered channel [11,12,13]
We propose optimal etching profiles that can improve the uniformity of the electrical characteristics between cells were proposed, and we discuss the reasons for changes in the threshold voltage shift (∆VT) due to changes in the etching profile
Summary
TWO-dimensional (2-D) flash memory technologies have faced physical limitations due to the shrinking problem of NAND flash memories [1], [2]. When implementing multi-level technology and high-rise stacking technology to enhance efficiency, several factors affect the variability of 3-D NAND flash memories, and these factors can be classified into three categories [5]: the effect of grain boundary traps [6,7,8,9], fluctuations in the control of the critical dimension [10], and the effect of the tapered channel [11,12,13] Among these factors, the taper angle and the mold height are major reasons for the string performance differences between the top and the bottom cells as the number of cells is increased. We propose optimal etching profiles that can improve the uniformity of the electrical characteristics between cells were proposed, and we discuss the reasons for changes in the threshold voltage shift (∆VT) due to changes in the etching profile
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