Three-dimensional memory device with plural channels per memory opening and methods of making the same

A three-dimensional memory device comprising a memory die that includes:

• an alternating stack of insulating layers and electrically conductive layers;
• memory openings vertically extending through the alternating stack;
• memory opening fill structures located in the memory openings, wherein each of the memory opening fill structures comprises a memory film and two vertical semiconductor channels, and the memory openings and the memory opening fill structures are arranged in rows that laterally extend along a first horizontal direction and are laterally spaced from each other along a second horizontal direction;
• and
• drain-select-level dielectric isolation structures extending through each row of the memory opening fill structures at least at a level of a topmost one of the electrically conductive layers;
• wherein:
• each of the drain-select-level dielectric isolation structures has a uniform width along the second horizontal direction and contacts bottom surfaces of a respective row of the drain regions that is arranged along the first horizontal direction;
• and
• each of the memory opening fill structures comprises a dielectric core contacting inner sidewalls of the two vertical semiconductor channels and contacting a pair of lengthwise sidewalls and a bottom surface of a respective one of the drain-select-level dielectric isolation structures.