Three-dimensional memory device with dielectric fins in staircase region and methods of making thereof

Abstract

A memory device is formed by forming an alternating stack of insulating layers and sacrificial material layers over a substrate, forming memory openings through the alternating stack, forming memory opening fill structures in the memory openings, forming an access trench through a portion of the alternating stack forming an access trench fill structure in the access cavity, and iteratively performing multiple instances of a unit processing sequence. Each instance of the unit processing sequence includes a vertical recess etch step that vertically recesses the access trench fill structure and an isotropic etch step that isotropically recesses the sacrificial material layers. A finned access cavity is formed after the multiple instances of the unit processing sequence. A finned dielectric support structure is formed in the finned access cavity, and the sacrificial material layers are replaced with electrically conductive layers.