A methodology for mechanical stress and wafer warpage minimization during 3D NAND fabrication

Abstract

The introduction of the 3D NAND architecture brought new integration challenges, including the impact of fabrication-induced mechanical stress. If not controlled, the mechanical stress can result in high wafer warpage, incompatible with wafer handling and lithography steps. This work presents a study of the impact of annealing on the warpage and residual stress of blanket SiO2/Si3N4 stacks relevant to 3D NAND fabrication. It is shown that annealing promotes H outgassing from the Si3N4 layers and minimizes their residual stress. The optimal temperature is calculated by combining the warpage measurements with finite element modelling. That allows to calibrate the model on simplified samples and then expand it for stacks with a higher number of layers, which can be beneficial for the future 3D NAND generations.