Multilevel memory stack structure and methods of manufacturing the same

A monolithic three-dimensional memory device comprising:

• a lower stack structure comprising a first stack of alternating layers including first electrically insulating layers and first electrically conductive layers and located over a substrate;
• at least one dielectric material layer overlying the lower stack structure;
• an upper stack structure comprising a second stack of alternating layers including second electrically insulating layers and second electrically conductive layers and located over the at least one dielectric material layer;
• a memory opening extending through the second stack, the at least one dielectric material layer, and the first stack;
• a memory film and at least one semiconductor channel located within the memory opening;
• and
• at least one via contact structure vertically extending through the upper stack structure, the at least one dielectric material layer, and a portion of the lower stack structure, and electrically shorted to at least one conductive structure located in, or underneath, the first stack;
• wherein the at least one via contact structure comprises:
• a first via contact portion embedded within the lower stack structure;
• and
• a second via contact portion embedded within the upper stack structure.