Three-dimensional memory device including backside trench support structures and methods of forming the same

A method of forming a three-dimensional memory device, comprising:

• 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, wherein each of the memory opening fill structures comprises a respective vertical semiconductor channel and a respective vertical stack of memory elements;
• forming a contact-level dielectric layer over the alternating stack;
• forming backside trenches laterally extending along a first horizontal direction through the contact-level dielectric layer and the alternating stack to form layer stacks including a respective patterned portion of the contact-level dielectric layer and a respective patterned portion of the alternating stack which are laterally spaced from each other by the backside trenches;
• forming a row of backside trench bridge structures that are laterally spaced from each other along the first horizontal direction within each of the backside trenches, wherein the backside trench bridge structures are more distal from the substrate than a most distal one of patterned portions of the sacrificial material layers is from the substrate;
• and
• replacing the patterned portions of the sacrificial material layers with electrically conductive layers.