NAND flash memory technologies have changed from two-dimensional (2D) to three-dimensional (3D) structures to solve scaling issues in 2D structures such as cell-to-cell interference problems. Several 3D NAND flash memories such as BiCS, P-BiCS, TCAT, VG-NAND, and SMArT have been previously presented. Contrary to a 2D structure, channels are formed in a 3D structure after filling inner layers of vertical cylindrical memory holes. Because these channels should be vertically formed in the 3D structure, channel materials have been changed from single-crystal silicon to poly-silicon (poly-Si). However, poly-Si channels exhibit critical issues such as low effective channel mobility, threshold voltage instability, and poor reliability. These problems are known to be primarily due to the defects, generated at the grain boundary of the poly-Si channel, which interrupt the current conduction.
In our study, we strive to improve the material properties of poly-Si channels for 3D NAND flash memory devices.