Investigation of Reducing Bow during High Aspect Ratio Trench Etching in 3D NAND Flash Memory

One challenge of high aspect ratio etching in 3D NAND flash memory is to maintain the perpendicularity of the etching profile. In this paper, a method is proposed to reduce bow during high aspect ratio trench etching. Bottom critical dimension/top critical dimension (BT) ratio and bow critical dimension (CD) are two pivotal parameters. This work focuses on the etching of SiO ₂ /SiN _x trench with aspect ratio larger than 50:1. By studying multiple influencing factors especially the function of different gas matching in every step, bow CD is improved while maintaining BT ratio in expectation.