Three-dimensional device with bonded structures including a support die and methods of making the same

A method of forming a bonded assembly, comprising:

• providing a memory die comprising a memory-side substrate, an alternating stack of insulating layers and electrically conductive layers that has stepped surfaces and is located on the memory-side substrate, memory stack structures vertically extending through the alternating stack, a stepped dielectric material portion contacting the stepped surface of the alternating stack, a through-dielectric external connection via structure vertically extending through the stepped dielectric material portion, memory-side metal interconnect structures included in memory-side interconnect-level dielectric layers, and memory-side bonding pads;
• providing a logic die comprising a semiconductor substrate, semiconductor devices located on the semiconductor substrate and including a peripheral circuitry configurated to control operation of the memory stack structures within the memory die, logic-side metal interconnect structures included in logic-side interconnect-level dielectric layers, and logic-side bonding pads;
• bonding the memory-side bonding pads to the logic-side bonding pads, wherein a die-to-die bonding interface is formed;
• physically exposing a distal planar surface of the through-dielectric external connection via structure by removing at least a portion of the memory-side substrate;
• and
• forming an external bonding pad on the distal planar surface of the through-dielectric external connection via structure.