Three-dimensional memory device with dielectric wall support structures and method of forming the same

A three-dimensional memory device, comprising:

• an alternating stack of insulating layers and electrically conductive layers located between a first line trench and a second line trench that laterally extend along a first horizontal direction and over a substrate;
• a first memory array region and a second memory array region that are laterally spaced apart along the first horizontal direction and including each layer of the alternating stack, wherein a respective set of memory stack structures each comprising a vertical semiconductor channel and a memory film vertically extends through the alternating stack within each of the first memory array region and the second memory array region;
• a first dielectric wall structure and a second dielectric wall structure that are located between the first line trench and the second line trench and between the first memory array region and the second memory array region, laterally extending along the first horizontal direction, and having a respective lateral extent along the first horizontal direction that is less than a lateral extent of the first line trench along the first horizontal direction, and is less than a lateral extent of the second line trench along the first horizontal direction, wherein a connection region is located between the first line trench and the first dielectric wall structure, and a staircase region is located between the second line trench and the second dielectric wall structure, and the electrically conductive layers of the alternating stack have lateral extents along the first horizontal direction that decrease in a vertical direction with an increase in a vertical distance away from the substrate;
• and
• an alternating stack of dielectric material plates and insulating plates or layers located between the first dielectric wall structure and the second dielectric wall structure, wherein the dielectric material plates have horizontal cross-sectional areas that decrease in the vertical direction with an increase in the vertical distance away from the substrate.