Three-dimensional memory device containing auxiliary support pillar structures and method of making the same

A three-dimensional memory device includes a first-tier structure located over a substrate and including a first alternating stack of first insulating layers and first electrically conductive layers. a second-tier structure located over the first-tier structure and including a second alternating stack of second insulating layers and second electrically conductive layers, memory stack structures vertically extending through the first alternating stack and the second alternating stack, primary support pillar structures, and auxiliary support pillar structures vertically extending through the first alternating stack, underlying the second stepped surfaces, and located below a horizontal plane including a bottommost surface of the second alternating stack.