Improvement of warpage and leakage for 3D NAND flash memory

Abstract

GLS (Gate line split) filling is a very important process in 3D NAND flash memory (3D NAND) fabrication. Filling materials in the GLS should have threefold properties, such as warpage tunability, leakage-free and low resistance. In this paper, the effects of different GLS filling materials (SiO2, W, amorphous silicon: A-Si) on F-attack, warpage and resistance were studied. GLS filled with A-Si shows best performance on warpage and F-attack. For 3D NAND, the number of stacked layers is predicted as a function of the wafer warpage, and the wafer warpage difference between GLS filled with A-Si and W was compared. With the same number of stacking layers, the wafer warpage post GLS filled with A-Si is smaller than that filled with W. Meanwhile, A-Si is produced by the decomposition of SiH4 by low pressure chemical vapor deposition (LPCVD) process, F-related by-product in the GLS filling material and consequent ACS (array common source) to WL (Word line) leakage by F-attack are avoided. A-Si is the best choice for GLS filling. This work provides an efficient method to solve the warpage and leakage problem in 3D NAND flash memory fabrication.